I prayed with the Messenger of Allah ﷺ, and when he prostrated I could see the whiteness of his armpits.
أخبرنا علي بن حجر قال أنبأنا إسمعيل قال حدثنا داود بن قيس
صليت مع رسول الله ﷺ فكنت أرى عفرة إبطيه إذا سجد
No references are available.
Its isnad is sahih. Tirmidhi reported it in his chapter on prayer, in the chapter on what has been said about spreading the arms away from the body in sujud, hadith no. 274, from the hadith of Dawud with this account, and he said, "Hasan, we do not know it except through the hadith of Dawud bin Qays." It is also found in Kubra, hadith no. 695.