مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3173
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The whiteness of the armpits of the Messenger Allah (ﷺ) could be seen when he prostrated.
Musnad Ahmad 3197Saheeh because of corroborating evidence, its isnad is da’ee