مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2518
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The back of an onager - or the leg of an onager was given to the Messenger of Allah (ﷺ) when he was in ihram, and he refused it.
Musnad Ahmad 2530Its isnad is saheeh, Muslim (1194)]