When the Prophet (ﷺ) prostrated he would hold his arms out from his sides so that if a lamb wanted to pass beneath his arms it would be able to do so.
Sunan an-Nasa'i Book 12, Hadith 81
← Previous Hadith "I prayed with the Messenger of Allah (ﷺ) and I used to see the whiteness of his armpits when he prostrated."

Sunan an-Nasa'i Book 12, Hadith 80 Next Hadith → "I heard Anas (narrate) that the Messenger of Allah (ﷺ) said: 'Be moderate in prostration and do not rest your forearms along the ground like a dog.'"

Sunan an-Nasa'i Book 12, Hadith 82