It is narrated from Sayyiduna Abu Kabshah al-Anmari (may Allah be pleased with him) that he came to a man and said: Lend me your horse (for breeding), for I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever lends his horse to a Muslim (for breeding) and (the mare) conceives from that horse, he will have a reward like that of seventy horses given for riding in the path of Allah; and if she does not conceive, he will have a reward like that of one horse given for riding in the path of Allah."
Hadith Referenceالمعجم الكبير للطبراني / مسند من يعرف بالكنى / 19056