Any Difference between ‘In Sha Allah’ and ‘Bi Idhnillah’?
Question

Which is better when I say that I am going to do something – should I say “Bi idhnillah (by Allah’s leave)” or “In sha Allah (if Allah wills)”? Which of them is better, whether it has to do with my worldly affairs or religious affairs? Or is the matter subject to further discussion, so that regarding my religious affairs, for example, I should say “Bi idhnillah” and regarding my worldly affairs, I should say “In sha Allah”? Or is there no difference?
Praise be to Allah.We do not think there is any difference between you saying “In sha Allah ” or “Bi idhnillah.” That is for several reasons, the most important of which are:
Firstly:
What is meant by both phrases is very similar, so making something conditional upon Allah’s will is similar to making it conditional upon His leave or permission. This is because both the general will of Allah and His universal leave and decree are both characteristics of divine Lordship that belong to the Creator, may He be glorified and exalted. Whatever Allah wills, He has permitted it to happen, and whatever He has permitted to happen, He has willed that it be created and brought into existence. Thus the two meanings are synonymous.
Secondly:
The Quranic usage of these two phrases is also very close in meaning, and we do not see any difference between their meanings, as they are always used in the same context. Allah, may He be exalted, says (interpretation of the meaning):
{It has never been for us to bring you evidence except by permission of Allah.} [Ibrahim 14:11]
{And it was not for a messenger to come with a sign except by permission of Allah.} [ar-Ra‘d 13:38]
With regard to His will, Allah, may He be exalted, says (interpretation of the meaning):
{Blessed is He who, if He willed, could have made for you [something] better than that - gardens beneath which rivers flow - and could make for you palaces.} [al-Furqan 25:10]
In fact, in the Quran there are some verses which mention both phrases together, which is indicative of how close they are in meaning. We see this in the verses in which Allah, may He be glorified and exalted, says (interpretation of the meaning):
{And it is not for any human being that Allah should speak to him except by revelation or from behind a partition or that He sends a messenger to reveal, by His permission, what He wills. Indeed, He is Most High and Wise.} [ash-Shura 42:51]
{And how many angels there are in the heavens whose intercession will not avail at all except [only] after Allah has permitted [it] to whom He wills and approves.} [an-Najm 53:26]
Thirdly:
We have not come across anyone among the mufassirin, scholars of ‘aqidah and commentators on hadith who differentiates between the two phrases; rather we have found those who interpret the divine will as referring to Allah’s leave or permission.
Al-‘Allamah at-Tahir ibn ‘Ashur (may Allah have mercy on him) said:
“What is meant by the divine will is Allah’s permission.” (At-Tahrir wa’t-Tanwir (15/296)
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said:
“Allah’s permission is of two types: universal (kawni) and religious (shar‘i). They have been explained previously in the verse (interpretation of the meaning): {it is [none but] he who has brought the Quran down upon your heart, [O Muhammad], by permission of Allah} [al-Baqarah 2:97].” (Tafsir al-Fatihah wa’l-Baqarah, 3/36)
The fuqaha have a topic called al-istithna (condition; it refers to saying “In sha Allah (if Allah wills)”) in which they discuss oaths, vows, divorce (talaq) and so on. They say: That is when you connect something to the will of Allah and the like, which renders the ruling invalid, as it says in al-Mawsu‘ah al-Fiqhiyyah (7/278). And they say: When you say “bi idhnillah,” it leads to the same outcomes as saying “in sha Allah .”
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked the following question: Is it permissible to make a condition in an oath by saying words other than “in sha Allah,” such as saying “Bi idhnillah (by Allah’s leave)”?
He replied:
“Yes, that is permissible, because saying “bi idhnillah” is like saying “in sha Allah.” (Liqa al-Bab al-Maftuh (no. 119, question no. 18)
And Allah knows best.