Sahih Muslim 1105
صحيح مسلم#1105SahihAbdullah b. Malik ibn Bujainah reported:When the Prophet (ﷺ) prostrated, lie spread out his arms so that the whiteness of his armpits was visible
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 4:267