Musnad Ahmad 20:14

Wahb ibn Jarir narrated to us, my father narrated to us, he said: I heard Muhammad ibn Abi Ya’qub narrating from al-Hasan ibn Sa’d, from ‘Abdullah ibn Ja’far, who said: The Messenger of Allah (peace and blessings of Allah be upon him) mounted his mule, and he let me ride behind him. When the Messenger of Allah (peace and blessings of Allah be upon him) would relieve himself, the most beloved thing for him to relieve himself in was a mound that would conceal him, or a palm orchard. He entered an orchard belonging to a man from the Ansar, and there was a camel used for irrigation in it. When it saw the Prophet (peace and blessings of Allah be upon him), it groaned and its eyes shed tears. The Messenger of Allah (peace and blessings of Allah be upon him) dismounted and wiped its ears and its hump, so it calmed down. He then said: "Who is the master of this camel?" A young man from the Ansar came and said: "I am." He said: "Do you not fear Allah regarding this beast which Allah has placed in your possession? For it has complained to me, claiming that you starve it and exhaust it." Then the Messenger of Allah (peace and blessings of Allah be upon him) went into the orchard and relieved himself, then performed ablution, then came while water was dripping from his beard onto his chest. He whispered something to me that I will not tell to anyone. We pressed him to tell us, but he said: "I will not disclose the secret of the Messenger of Allah (peace and blessings of Allah be upon him) until I meet Allah."