One objection to this answer remains:

If the Book of Allah requires the fulfilment of conditions in general, then a condition concerning patronage falls within that general rule.

The answer is:

A general text applies only where no specific evidence excludes the case in question, for the specific clarifies the general. The Prophet, may Allah bless him and grant him peace, ruled out this stipulated arrangement by prohibiting the sale or gift of patronage and by saying:

“Whoever claims descent from someone other than his father, or takes patrons other than his own, upon him is the curse of Allah, the angels, and all people.”

The Book also indicates this in the words of Allah Most High:

“Allah has not placed two hearts within any man’s body, nor has He made your wives whom you liken to your mothers your mothers, nor has He made your adopted sons your own sons. These are merely words you utter with your mouths. Allah speaks the truth, and He guides to the right way.”

“Call them after their fathers; that is more just in the sight of Allah. If you do not know their fathers, then they are your brothers in faith and those bound to you by patronage.”

He thus made it obligatory for us to ascribe a person to the father who begot him, rather than to the man who adopted him, and prohibited adoption. He then commanded that, when the father is unknown, the person be called a brother in faith and one bound by patronage, just as the Prophet, may Allah bless him and grant him peace, said to Zayd ibn Hārithah:

“You are our brother and our freedman.”

He also said, may Allah bless him and grant him peace:

“Your servants are your brothers whom Allah has placed under your authority. Whoever has his brother under his authority should feed him from what he himself eats and clothe him from what he himself wears.”

Thus He, glorified be He, made patronage analogous to lineage and explained the basis of patronage in His words: