Sunan Ibn Majah, Volume 3, Book 8, Hadith 1813 (DarusSalam) ⓘ
Ali narrated that: the Messenger of Allah said: “I have exempted you from having to pay Sadaqah on horses and slaves.”
حَدَّثَنَا سَهْلُ بْنُ أَبِي سَهْلٍ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْحَارِثِ، عَنْ عَلِيٍّ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ " تَجَوَّزْتُ لَكُمْ عَنْ صَدَقَةِ الْخَيْلِ وَالرَّقِيقِ " .
also referenced under: Hadith 1813 (Reference) & Book 8, Hadith 31 (In-Book)