Sunan At-Tirmidhi

Ubaidallah bin Abdullah bin Arqam Al-Khuza'I narrated from his father (Abdullah bin Arqam), who said:""I was with my father at the plains of Namirah. I passed by a mount and saw Allah's Messenger standing in Salat."" He said: ""I was looking at the earthiness of his armpits when he prostrated."" [That is]: ""Whiteness