when one of you prostrates himself, he should not stretch out his forearms( on the ground) like a dog and he should join both of his thighs.
Sunan Abi Dawud Book 2, Hadith 511
← Previous Hadith When the Messenger of Allah (ﷺ) prostrated himself, he kept his arms far away from his sides so much so that we took pity on him.

Sunan Abi Dawud Book 2, Hadith 510 Next Hadith → The Companions of the Prophet (ﷺ) complained to the Prophet (ﷺ) about the hardship when they kept their forearms far away from their sides while prostrating. He said: Take help with the elbows (by spreading them on the ground and sticking them to the sides).

Sunan Abi Dawud Book 2, Hadith 512