Abdullah bin Ubaydullah bin al-Abbas said: We were sitting with Ibn Abbas (may Allah be pleased with them both) among some young men of Banu Hashim, and he said: By Allah, the Prophet (peace and blessings be upon him) did not single us out for anything to the exclusion of other people except three things: "He commanded us to perform ablution thoroughly, he commanded us not to eat charity, and not to mate donkeys with horses."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13236