Musnad Ahmad 31:894

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Yahya ibn Abi Kathir, from Abu Salamah ibn 'Abd al-Rahman, from Abu Sa'id al-Khudri: "That he saw mud on the nose of the Messenger of Allah, may Allah bless him and grant him peace, and on the tip of his nose, from the traces of prostration, and they had been rained upon during the night."