'Abdullah b. Malik ibn Bujainah reported
When the Prophet (ﷺ) prostrated, lie spread out his arms so that the whiteness of his armpits was visible.
This hadith has been narrated by Ja'far b. Rabi' with the same chain of transmitters. And in the narration transmitted by 'Amr b. al-Harith (the words are)
" When the Messenger of Allah (rtiay peace be upon him) prostrated, he spread out his arms so that the whiteness of his armpits was visible." And in the narration transmitted by al-Laith (the words are:" When the Messenger of Allah (ﷺ) prostrated. he spread his hands from the armpits so that I saw their whiteness."
Maimuna reported
When the Messenger of Allah (ﷺ) prostrated himself, if a lamb wanted to pass between his arms, it could pass.
Maimuna, the wife of the Messenger of Allah (ﷺ), reported
When the Messenger of Allah (ﷺ) prostrated himself, he spread his arms, i. e. he separated them so much that the whiteness of his armpits became visible from behind and when he sat (for Jalsa) he rested on his left thigh.
Maimuna daughter of Harith reported
When the Messenger of Allah (ﷺ) prostrated, he kept his hands so much apart from each other that when it was seen from behind the armpits became visible. Waki' said: That is their whiteness.
'A'isha reported
The Messenger of Allah (ﷺ) used to begin prayer with takbir (saying Allahu Akbar) and the recitation: "Praise be to Allah, the Lord of the Universe." When he bowed he neither kept his head up nor bent it down, but kept it between these extremes; when he raised his head after bowing he did not prostrate himself till he had stood erect; when he raised his head after prostration he did not prostrate himself again till he sat up. At the end of every two rak'ahs he recited the tahiyya; and he used to place his left foot flat (on the ground) and raise up the right; he prohibited the devil's way of sitting on the heels, and he forbade people to spread out their arms like a wild beast. And he used to finish the prayer with the taslim.