Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) regarding "And give them from the wealth of Allah which He has given you" [Surah al-Nur: 33]; he (peace and blessings be upon him) said: "A quarter of the kitabah." In the narration of Abu Abdullah: "He should leave a quarter for the mukatab."
Hajjaj bin Muhammad added: Ibn Jurayj said: More than one of those who heard this hadith from Ata' bin al-Sa'ib told me that he did not attribute it to the Prophet (peace and blessings be upon him). Ibn Jurayj said: But he attributed it to him when narrating to me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21667