Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: One day the Prophet (peace and blessings be upon him) was sitting with the people around him (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Indeed, Allah Almighty has made for every prophet something he delights in, and what I delight in is standing in prayer at night. When I stand to pray, let no one stand (in prayer) behind me. And Allah Almighty has given every prophet a provision, and my provision is this one-fifth (khums). When I pass away, it will go to those in authority after me."
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain mentions that it was narrated by Ishaq bin Abdullah bin Kaysan (from his father). Abu Hatim declared him (Ishaq) weak, and his father was declared thiqah (trustworthy) by Yahya bin Ma'in, while Abu Hatim and others declared him da'if (weak).