llah, most Gracious, most Merciful
Praise be to Allah alone and peace and prayers be upon the Messenger of Allah after whom there is no other prophet, and upon his family, Companions and those who follow him in piety until the Day of Judgment

We reviewed request no. 477 for the year 2006 which includes the following:
What is the ruling for 'asab al-fahl? A horse owner owns a rare horse breed and rents his stallions to those who wish to breed their mares to his studs for a predetermined fee.
 

Scholars are unanimous on the impermissibility of selling 'asab al-fahl (stud semen). They based their opinion on the hadith of 'Abdullah Ibn 'Umar (may Allah be pleased with him) who said, "The Messenger of Allah prohibited [the sale of] 'asab al-fahl" [Bukhari]. This is because at the time of agreement, 'asab al-fahl is non-existent and the sale of a non-existent object is invalid.
In contrast, there is a scholarly debate on the permissibility of renting stallions for breeding. The majority of scholars have maintained its prohibition due to the above mentioned hadith prohibiting the sale of 'asab al-fahl (and, by extension, the prohibition of renting studs for breeding). Hanbali scholars and 'Ata`, have maintained the permissibility of renting studs to breed mares if a person cannot find anyone to offer this service for free. According to them, only the recipient of the fee is blameworthy.
Maliki scholars (in their opinion which is analogous to the fair opinion of the Shafi'i school), Abu Al-Khattab from among the Hanbalis, al-Hasan Al-Basri and Ibn Sirin, have all maintained the permissibility of renting stallions for breeding. We are inclined to agree with this opinion for the following reasons:
- The speculative nature of the above mentioned proof;
- The necessary permissible benefit accrued from renting studs for breeding;
- The ruling is based on the permissibility of hiring a wet nurse and is analogous to the permissibility of loaning studs for breeding.
It is important to note that the rent period must be determined. It is impermissible to rent a stud for an undetermined period, such as until the mare is impregnated, as Maliki scholars and others have maintained.
Allah the Almighty knows best.