Tafsir of Al Imran 3:122

(When two parties among you intended) It is said: This is a substitute for the phrase "When you set out" (idh ghadawta), clarifying the intended meaning behind the reminder. It is also permissible for it to be an adverbial modifier to the act of "settling" (tabwi’), or "when you set out" (ghadawta), or "All-Knowing" (‘aliman), by way of contention (tanazu’), or for all of them combined in one view. It is not intended to restrict His being All-Hearing and All-Knowing to that specific time.

(Two parties among you) meaning two groups of Muslims. They were two clans of the Ansar: Banu Salama from the Khazraj and Banu Haritha from the Aws. They were the two wings of the Messenger of Allah’s (may Allah’s peace and blessings be upon him) army. This was stated by Ibn Abbas, Jabir ibn Abdullah, al-Hasan, and a great multitude. Al-Jubba’i said: A party from the Emigrants (Muhajirun) and a party from the Helpers (Ansar).

(To fail) meaning to weaken and become cowardly when they saw the desertion of Abdullah ibn Ubayy ibn Salul and those with him from the Messenger of Allah (may Allah’s peace and blessings be upon him). The construction formed by the particle an and the verb is connected to them, with the preposition ba omitted; that is: they intended to fail (hammata bil-fashal). The intended meaning here is the consequence of the optional action upon which the intention rests. It is apparent that this intention did not arise from a firm resolve or determination to oppose the Prophet (may Allah’s peace and blessings be upon him) and abandon him, for such a thing would not proceed from a believer; rather, it was merely an internal discourse and a whispering of the soul, like the saying: "I say to it when it heaves and boils: Stay where you are, you will be praised or relieved." This is supported by the Almighty’s saying: (And Allah is the Protector of both) meaning their Supporter. The sentence is a parenthetical clause.

It is also permissible for it to be a circumstantial qualifier (hal) for the subject of "intended" or its pronoun in "to fail," conveying the improbability of their failing or intending such while they were under the guardianship of Allah the Exalted. Abdullah [ibn Mas’ud] recited: "And Allah is their Protector" (wallahu waliyyuhum) using the plural pronoun, along the lines of [the verse]: "And if two parties of the believers fight one another."

(And upon Allah let the believers rely) meaning upon Him, Exalted is He, and not upon anyone else, as is signified by placing the object before the verb and using the Majestic Name (Allah) to seek blessing through it and to provide the reasoning. The al- in "the believers" is for the genus, and the two parties are included therein as a primary matter. In this title, there is an indication that faith in Allah the Exalted is one of the causes of relying upon Him. The object of reliance has been omitted to convey generality; that is, let them rely upon Him, Glorified is His status, in all of their affairs—the significant and the trivial, the easy and the difficult.