1. Iftiraq is the severest form of ikhtilaf; in fact it is [one of] the consequences of ikhtilaf. This is because sometimes ikhtilaf may reach the level of ikhtilaf and sometimes it may not, hence iftiraq is ikhtilaf and something extra. However, not every ikhtilaf is iftiraq and upon this is built the second difference.
2. Not every ikhtilaf is iftiraq while every iftiraq is ikhtilaf. Many of the matters that the Muslims differ over are from the matters of ikhtilaf [but not iftiraq]. It is not permissible to pronounce upon the one who differs [with you] on such issues the ruling of kufr (disbelief), of being one who has split [from the Jama'ah], or of being one who has departed from the sunnah.
3. Iftiraq does not occur except in issues of the usul ul-kubra (great principles), i.e., the principles of the religion wherein there is no leeway for differing. These are such principles as are affirmed by a clear and definitive text, or by a consensus (ijma'), or a methodology of Ahlus-Sunnah wa'l-Jama'ah in which there is no difference [of opinion]. So whatever is like this, then it becomes a principle ('asl) and whoever differs concerning it has become one who splits (muftariq) [from the Jama'ah]. As for anything other than that, then it falls under a category of ikhtilaf. So ikhtilaf occurs in those issues that are not from the usul, for which a number of opinions are allowed just as ijtihad is [also] allowed, all of this is possible.
The proponent [of each opinion] could have his proofs, just as he could have given that ruling out of ignorance, coercion, or [incorrect] interpretation; this holds for the matters of ijtihad and the subsidiary issues (far'iyyat). It can also hold for some issues of usul which [may be], due to 'awaridh [obstacles], excused in the eyes of the Imams whose opinions are taken into consideration.
So the subsidiary issues sometimes occur in some matters of belief, which, in their principles are agreed upon, but are differed upon in their details. For example, the consensus of the Imams on the occurrence of the mi'raj, and their ikhtilaf and disputes about the Messenger, peace be upon him, seeing his Lord. Was it with his eyes or his heart?
4. Ikhtilaf could occur due to ijtihad and good intention. The one who errs [in issues of ikhtilaf] is rewarded whilst he is searching for the truth. The one who is correct gets more reward and indeed, the one who errs is praised for his ijtihad also. When it reaches the level of iftiraq, then it is blameworthy in its entirety. Similarly, iftiraqcannot occur upon an ijtihador a correct intention. The one who splits is not rewarded, but is blameworthy and is a sinner under all circumstances. From this [we can understand] that [iftiraq] does not occur except by his innovating, following his desires, or blameworthy blind following.
5. Iftiraq is connected with the threat [of punishment]. All of it is misguidance and [leads to] his destruction. As for ikhtilaf, then this is not the case. [This is] provided that the ikhtilaf between the Muslims is in those matters which ijtihad is allowed, or the person is a person who is following an opposing opinion, but he has certain legitimate factors [that lead him to hold that opinion]. [Similarly] it is possible that he held that opposing opinion out of ignorance of the evidence, and the proof has not been established against him. He may have held that opinion out of coercion for which he is excused even if [his coercion] was not witnessed by anybody, or due to misinterpretation and this cannot be ascertained except after establishing the proofs [against him].
Translation by Abu Abdis-Salaam