He is asking about the reason for the difference of opinion among the scholars about saying the name of Allah at the time of slaughter
Question

                What is ruling on saying the name of Allah at the time of slaughter?

I would like to know the opinions of the scholars in detail, and their response to opinions that differ from theirs. I read fatwa no. 85669, and was impressed by it, but I want to know the evidence for the prohibition on that over which the name of Allah was not mentioned, and details of scholarly opinions, especially the Shaafa‘i view. I am also confused about the fact that Allah restricts what is prohibited in the verse in which He says (interpretation of the meaning):

“He has forbidden you only the Maytatah (dead animals), and blood, and the flesh of swine, and that which is slaughtered as a sacrifice for others than Allah. But if one is forced by necessity without wilful disobedience nor transgressing due limits, then there is no sin on him. Truly, Allah is Oft-Forgiving, Most Merciful”

[al-Baqarah 2:173]

“Say (O Muhammad (blessings and peace of Allah be upon him)): I find not in that which has been inspired to me anything forbidden to be eaten by one who wishes to eat it, unless it be Maytatah (a dead animal) or blood poured forth (by slaughtering or the like), or the flesh of swine (pork, etc.) for that surely is impure, or impious (unlawful) meat (of an animal) which is slaughtered as a sacrifice for others than Allah. But whosoever is forced by necessity without wilful disobedience, nor transgressing due limits, (for him) certainly, your Lord is OftForgiving, Most Merciful”

[al-An‘aam 6:145].

But it does not mention that over which the name of Allah was not mentioned.
Praise be to Allah.
		Firstly:

	The scholars differed concerning the ruling on mentioning the 
	name of Allah at the time of slaughter, and there are several views:

	The Hanafis, Maalikis and Hanbalis – according to the 
	well-known view among them – are of the view that mentioning the name of 
	Allah at the time of slaughter is obligatory, but if it is omitted by 
	mistake or if one forgets, then the meat is still permissible. They quoted 
	as evidence for it being obligatory the verse in which Allah, may He be 
	exalted, says (interpretation of the meaning):

	“Eat not (O 
	believers) of that (meat) on which Allah’s Name has not been pronounced (at 
	the time of the slaughtering of the animal), for sure it is Fisq (a sin and 
	disobedience of Allah)”

	[al-An‘aam 6:121].

	The idea that the ruling is waived in the case of forgetting 
	is based on the general meaning of the words of the Prophet (blessings and 
	peace of Allah be upon him): “Allah has forgiven my ummah for their mistakes 
	and forgetfulness, and what they are forced to do.” 

	Narrated by Ibn Maajah (2043); classed as saheeh by al-Albaani 
	in Saheeh Ibn Maajah.

	The Shaafa‘is were of the view – which is also mentioned in 
	one report from Ahmad – that mentioning the name of Allah at the time of 
	slaughter is Sunnah.

	They quoted as evidence the report narrated by al-Bukhaari 
	(5502) in which it says that a slave-woman belonging to Ka‘b ibn Maalik was 
	tending some sheep of his in the market in al-Jubayl, near Sal‘ [a mountain 
	in Madinah], and one sheep got injured, so she broke a stone and slaughtered 
	the sheep with it. They told the Prophet (blessings and peace of Allah be 
	upon him) about that and he told them to eat it.

	They also quoted as evidence the fact that Allah, may He be 
	exalted, has permitted meat slaughtered by the People of the book, as He, 
	may He be exalted, says (interpretation of the meaning): 
	“The 
	food (slaughtered cattle, eatable animals, etc.) of the people of the 
	Scripture (Jews and Christians) is lawful to you” 
	[al-Maa’idah 5:5], and 
	they do not mention the name of Allah at the time of slaughter.

	They also quoted as evidence the report narrated by al-Bayhaqi 
	(18890) from Ibn ‘Abbaas (may Allah be pleased with him) from the Prophet 
	(blessings and peace of Allah be upon him) who said: “His own name is 
	sufficient for the Muslim, and if he forgets to mention the name of Allah at 
	the time of slaughter, let him mention the name of Allah and eat it.” But 
	this is a da‘eef (weak) hadith; the correct view is that its isnaad ends 
	with Ibn ‘Abbaas [and it is not to be attributed to the Prophet (blessings 
	and peace of Allah be upon him)]. See: at-Talkhees al-Habeer (4/338)

	They responded to the supporters of the first view by noting 
	that the words of Allah (interpretation of the meaning), ““Eat 
	not (O believers) of that (meat) on which Allah’s Name has not been 
	pronounced (at the time of the slaughtering of the animal)” 
	[al-An ‘aam 6:121] are to be understood as referring to that which was 
	slaughtered for something other than Allah, as in the verse in which He says 
	(interpretation of the meaning): “or 
	impious (unlawful) meat (of an animal) which is slaughtered as a sacrifice 
	for others than Allah” 
	[al-An‘aam 6:145].

	Ibn Jurayj said, quoting from ‘Ata’ concerning the words, “Eat 
	not (O believers) of that (meat) on which Allah’s Name has not been 
	pronounced”: This is a 
	prohibition on meat that was slaughtered by Quraysh on behalf of the idols, 
	and on meat slaughtered by the Magians.

	The Zaahiris (literalists) were of the view that it is a 
	condition that cannot be waived under any circumstances, not even in the 
	case of forgetfulness, deliberate action or ignorance. This was narrated 
	from Maalik and Ahmad, and was the view of a group among the early 
	generations, and was the view favoured by Shaykh al-Islam Ibn Taymiyah. They 
	quoted as evidence for that the general meaning of the verse in which Allah, 
	may He be exalted, says (interpretation of the meaning), 
	“Eat 
	not (O believers) of that (meat) on which Allah’s Name has not been 
	pronounced” [al-An‘aam 
	6:121], and the fact 
	that the Prophet (blessings and peace of Allah be upon him) said: “If the 
	blood has been caused to flow and the name of Allah has been mentioned over 
	it, then eat.” Agreed upon.

	So it is stipulated in order for the food to be permissible 
	that the name of Allah should be mentioned, and it is well-known that if the 
	condition is not fulfilled, then that which is conditional upon it does not 
	come into effect. So if mentioning of Allah’s name is omitted, then the 
	permissibility of the meat does not come into effect. This is the case with 
	all conditions.

	See: al-Mawsoo‘ah al-Fiqhiyyah (8/90); Tafseer Ibn 
	Katheer (3/325); see also question no. 85669

	Al-Qurtubi (may Allah have mercy on him) stated in his 
	Tafseer (7/75) that there was a difference of scholarly opinion 
	concerning that.

	Secondly:

	The evidence for the prohibition on eating that over which 
	the name of Allah was not mentioned, according to those who say that doing 
	so is obligatory or is an essential condition, is the verse in which Allah, 
	may He be exalted, says (interpretation of the meaning): 
	“So 
	eat of that (meat) on which Allah’s Name has been pronounced (while 
	slaughtering the animal), if you are believers in His Ayat (proofs, 
	evidences, verses, lessons, signs, revelations, etc.)” 
	[al-An‘aam 6:118], as 
	well as the verse in which He may He be exalted, says (interpretation of the 
	meaning), “Eat 
	not (O believers) of that (meat) on which Allah’s Name has not been 
	pronounced” [al-An‘aam 
	6:121].

	Al-Qurtubi said:

	So He mentioned both scenarios and clarified both rulings. 
	The words “Eat not” indicate that it is haraam and should not be interpreted 
	as meaning that it is makrooh. However, with regard to one who omits it by 
	mistake or because of forgetfulness, he is not addressed here, so the 
	condition is not binding in his case.

	Tafseer al-Qurtubi 
	(7/76)

	Thirdly:

	Allah, may He be glorified and exalted, did not mention that 
	over which His name has not been mentioned among the things that He 
	prohibited in the verses in which He says (interpretation of the meaning):

	“He has 
	forbidden you only the Maytatah (dead animals), and blood, and the flesh of 
	swine, and that which is slaughtered as a sacrifice for others than Allah”

	[al-Baqarah 2:173]

	“Say (O 
	Muhammad (blessings and peace of Allah be upon him)): I find not in that 
	which has been inspired to me anything forbidden to be eaten by one who 
	wishes to eat it, unless it be Maytatah (a dead animal) or blood poured 
	forth (by slaughtering or the like), or the flesh of swine (pork, etc.) for 
	that surely is impure, or impious (unlawful) meat (of an animal) which is 
	slaughtered as a sacrifice for others than Allah”

	[al-An‘aam 6:145]. 

	But He does mention it in the verse in which He, may He be 
	glorified and exalted, says (interpretation of the meaning):

	“Eat not (O 
	believers) of that (meat) on which Allah’s Name has not been pronounced (at 
	the time of the slaughtering of the animal), for sure it is Fisq (a sin and 
	disobedience of Allah)”

	[al-An‘aam 6:121]

	The shar‘i rulings (concerning an issue) should be worked out 
	on the basis of all the evidence that is mentioned in the Qur’an and Sunnah, 
	not from some of it to the exclusion of others.

	This is similar to the issue of no mention being made in the 
	Qur’an of the prohibition on all wild animals that have fangs and all birds 
	that have talons, which is mentioned in the Sunnah, as was narrated by 
	Muslim (1934) from Ibn ‘Abbaas who said: The Messenger of Allah (blessings 
	and peace of Allah be upon him) forbade all wild animals that have fangs and 
	all birds that have talons.

	And Allah knows best.