The Prophet ﷺ used to fast during Shaban and Ramadan, and he would make a point of fasting on Mondays and Thursdays.
كان النبي ﷺ يصوم شعبان ورمضان ويتحرى صوم الاثنين والخميس.
Tirmidhi (745), Nasai (2187), Ibn Majah (1649, 1739), and Imam Ahmad (24508) narrated it, and Ibn Hibban (3643) graded it sahih. All of them narrated it from Thawr bin Yazid, from Khalid bin Madan, who said, Rabia bin Ghaz told us that he asked Ayesha about the fasting of the Messenger of Allah ﷺ, and she said (and then he mentioned the hadith). Except that Ahmad did not mention Rabia between Khalid bin Madan and Ayesha. The correct view is to include him.Tirmidhi said, This is a hasan gharib hadith from this angle. Rabia bin Ghaz is Rabia bin Amr Jurashi, whom Daraqutni and others deemed reliable, and his narration is hasan. This chain is among the soundest by which this hadith has been narrated. It has other chains in which there is disagreement, as Nasai and others have said, but what is sahih is not harmed by what is not sahih.