(Imām Bukhārī narrates): Muslim ibn Ibrāhīm narrated to us, he said: Hishām narrated to us, from Yahyā, from Abū Salamah, he said: I asked Abū Sa'īd al-Khudrī, may Allāh be pleased with him, about this, so he narrated that:

I saw the Messenger of Allāh ﷺ prostrating in water and mud, until I saw the mark of mud upon his forehead.