When the Messenger of Allah (ﷺ) prayed he held his arms out so much that the whiteness of his armpits appeared.
Sunan an-Nasa'i Book 12, Hadith 78
← Previous Hadith When the Messenger of Allah (ﷺ) prayed he would Jakhkha.

Sunan an-Nasa'i Book 12, Hadith 77 Next Hadith → "If I were in front of the Messenger of Allah (ﷺ) I would be able to see the whiteness of his armpits." (One of the narrators) Abu Mijlaz said: "It is as if he said that because he was praying."

Sunan an-Nasa'i Book 12, Hadith 79