Abdullah bin Ubaydullah says: I came to Ibn Abbas (may Allah be pleased with him) among some young men of Banu Hashim. Ibn Abbas (may Allah be pleased with him), in a hadith that he mentioned from the Prophet (peace and blessings be upon him), said that the Prophet (peace and blessings be upon him) "singled us out from others in three things: 1. that we complete the ablution (wudu); 2. that we do not eat charity (sadaqah); 3. that we do not let a donkey mount a mare."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السبق والرمي / 19789