Sunan Ibn Majah
1739
Sahih+2

It was narrated from Rabi’ah bin Ghaz that he asked ‘Aishah about the fasting of the Messenger of Allah (ﷺ). She said:“He used to make sure he fasted on Mondays and Thursdays.”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi