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

English translation · Jami' at-Tirmidhi