Condition of saying Bismillaah in order for meat to be halal
Question

What is the ruling on saying Bismillaah over the sacrifice, especially if the slaughterman does not pray?.
Praise be to Allah.Meat slaughtered by one who does not pray is not halal, whether he says the name of Allah over it or not. See question no. 70278. 
With regard to saying Bismillah when slaughtering meat, the fuqaha’ differed concerning that and there are three points of view: 
1 – That it is mustahabb only, which is the view of al-Shaafa’i. 
2 – That it is a condition of the meat being halal, but if a person forgets it by mistake it is still permissible. This is the view of the Hanafis, Malikis and Hanbalis.  
3 – That it is essential and cannot be waived under any circumstances, whether it is omitted by mistake or deliberately or out of ignorance. This is the view of the Zaahiris and was narrated from Maalik and Ahmad, and it was the view of some of the salaf; it was also the view favoured by Shaykh al-Islam Ibn Taymiyah. Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: It is the correct view. 
He also said: They quoted as evidence the general meaning of the verse in which Allah 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)” [al-An’aam 6:121]
And the Prophet (peace and blessings of Allah be upon him) said:  
“If the blood flows and the name of Allah is mentioned, then eat.” So in order for the meat to be halal, it is essential that the name of Allah be mentioned. It is well known that if the condition is not met, the thing is invalid, so if the name of Allah is not mentioned, the meat is not halal, as with any other condition. Hence if a person prays but he forgot to do wudoo’, he has to repeat the prayer. Similarly if he prays not realizing that he had broken his wudoo’ because he thought that breaking wind does not invalidate wudoo’, or that eating camel meat does not invalidate wudoo’, for example, then he must repeat it, because the thing is not valid without the conditions being met. So if he slaughtered it but the blood did not flow, by mistake or out of ignorance, then it is not halal, and the same applies if he does not mention the name of Allah, because it is mentioned in the same hadeeth. End quote from al-Sharh al-Mumti’ (6/358). 
See also: al-‘Inaayah Sharh al-Hidaayah (9/489); al-Fawaakih al-Dawaani (1/382); and al-Majmoo’ (8/387). 
Based on this, he should not slaughter sacrifices or anything else unless he is one of those who pray regularly, and it is essential that he mentions the name of Allah when slaughtering and says Bismillaah (in the name of Allah). 
It is also mustahabb to say takbeer, so he should say: Bismillaah, wa Allahu akbar (In the name of Allah and Allah is Most Great). 
Al-Bukhaari (5558) and Muslim (1966) narrated that Anas (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) sacrificed two horned black and white rams. I saw him placing his foot on their sides, and he said the name of Allah and he said takbeer, then he slaughtered them with his own hand. 
And Allah knows best.