What is the marriage of "hibah" (grant/donation)? What are its rulings? And what are the sayings of the Salaf concerning it?

Marriage by way of donation (Nikah al-Hibah) is when a woman donates herself to a man for marriage without a dowry. This was exclusively for the Prophet, peace and blessings be upon him alone, due to the Almighty's saying: "And [also for marriage] a believing woman if she gives herself to the Prophet [without dowry] and if the Prophet wishes to marry her—[this is] only for you, excluding the [other] believers." Scholars have unanimously agreed that a woman donating herself to anyone other than the Prophet is impermissible, except for what was narrated from Abu Hanifa and his two companions, who held that it is permissible if she donates herself and he (the husband) testifies to a dowry for himself. The Hanafis and Ibn Taymiyyah are of the view that marriage is contracted with the words of donation and ownership, provided that a dowry is stipulated.