The answer is two-fold.

First, denial: It does not follow from the Creator and the creature sharing the root of an attribute that they must be identical with respect to what is possible, impossible, or necessary for that attribute; mere participation does not entail likeness.

Second, concession: Grant, for the sake of argument, that your premise is valid. Even so, if the common element does not oblige us to affirm for the Lord—exalted is He—anything that is impossible for Him, nor to deny anything that is His due, then no contradiction arises. Thus, when they share in the attributes of existence, life, knowledge, and power, and each possessor of the attribute retains what properly belongs to him and befits him, their sharing is perfectly admissible and free of any objection. Indeed, affirming such a common element is required by the very notion of existence, for any two existents must have something of this sort in common. Whoever rejects that shared element is driven to deny the existence of everything, because negating what is common leads inevitably to absolute negation.

Whoever grasps this point thoroughly and reflects upon it will see that most doubts vanish, and he will recognize the error into which many intelligent people have fallen in this matter.

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Second line of evidence: Another indication that it is unsound to base the rule of negation solely on denying resemblance is that people differ over what constitutes resemblance; what one scholar labels resemblance another may not regard as such.

An illustration lies with the Muʿtazilites and others who follow their path of denial. They maintain that anyone who affirms for Allah, the Exalted, an eternal knowledge or an eternal power is guilty of tashbīh (likening), for in their view eternity is the Creator’s most exclusive attribute. Consequently, whoever affirms an eternal knowledge or power for Him has, in their estimation, posited for Him a counterpart.