Sayyiduna Aqram (may Allah be pleased with him) said: I was grazing goats in the plain of Namirah, and I saw the Messenger of Allah (peace and blessings be upon him) stop there. He (peace and blessings be upon him) established the prayer and led his Companions in prayer, and I prayed with them. It is as if I can still see the whiteness beneath the shoulders (the armpits) of the Messenger of Allah (peace and blessings be upon him) while he was in prostration.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 900