[Revocation by a Grandfather of his Transfer of Ownership to His Grandson]

Answer – and Allah is the One who grants success: If the grandfather has transferred property to his grandson with a valid transfer of ownership, then the grandson has acquired that property by virtue of that transfer. Based on this, it is not valid for the grandfather to retract and take back that property except with the willing consent of his grandson. This is due to the saying of the Prophet, May Allah bless him and his family and grant them peace: “The property of a Muslim is not lawful (for another) except with his willing consent.” And due to the saying of Allah the Exalted: “O you who believe, do not consume one another’s wealth in false ways, but only through trade by mutual consent.” [al-Nisāʾ:29]
And His saying, Exalted is He: “Give women their bridal gifts graciously; if they willingly forgo any part of it for you, then enjoy it in contentment.” [al-Nisāʾ:4] It is not valid to make an analogy between the grandfather and the father regarding the permissibility of retracting, because the father—as the jurists have said—is an exception to the normal rules of analogy; therefore, the grandfather and the mother are not to be analogized to him.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2