Tafsir of Yusuf 12:64

(He said, "Shall I entrust you with him...") An interrogative of disapproval. (I entrust you) with a prolongation and an open mim and a raf’ on the nun, an imperfect verb from the bab (form) of ‘alima (to know). Aminahu and i’tamanahu have the same meaning; that is, I do not entrust you with him, (except as I entrusted you) that is, except for a trust similar to my trust in you (with his brother) [Yusuf] (before). And you have already said regarding him what you said, then you did to him what you did; thus, I do not trust you, nor do I trust your preservation. I only entrust my affair to Allah the Exalted. (So Allah is the best guardian, and He is the Most Merciful of the merciful) I hope that He will have mercy on me by His preservation and not bring two afflictions upon me simultaneously.

This, as you see, is an inclination on his part—peace be upon him—toward granting permission and sending [the brother], when he saw the benefit in it. It also contains an evident level of reliance (tawakkul) upon Allah the Exalted. For this reason, it is narrated that Allah the Exalted said: "By My Might and My Majesty, I shall return them both to you, since you have relied upon Me."

(Guardian) is in the accusative case as a tamyiz (specification), similar to "To Allah belongs his merit as a horseman." Many have permitted that it be in the state of hal (circumstantial accusative). Abu Hayyan criticized this, arguing it is not sound because it restricts the "bestness" to this state, but it was countered that it is a permanent, emphatic hal, not one that defines/specifies, and there are many examples like it. Furthermore, it is an argument based on the concept of the "implied negative" (mafhum), which is not to be considered; and if it were to be considered, it would also be an objection against the tamyiz, and there is scrutiny in that.

Most of the seven readers read (preservation/guardian) with an accusative, and Abu al-Baqa stated it is exclusively tamyiz. Al-A’mash read (the best of guardians) with idafa (genitive construction) and the singular (guardian). Abu Hurairah read (the best of the guardians) with idafa and the plural. Ibn Atiyyah reported from Ibn Mas’ud—may Allah be pleased with him—that he read: "For Allah is the best of guardians, and He is the best of the guardians." Abu Hayyan said: "The sentence 'And He is the best...' should be interpreted as an explanation for the preceding sentence, not as Quranic text," and the justification for that has already passed.