Abu Qatadah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) was asked about fasting on Mondays. He said, "That is the day on which I was born and the day on which I received Revelation."[Muslim]. (PT)
App reference (PT): Book 9, Hadith 265 (PT)
Arabic/English book reference (PT): Book 9, Hadith 1255 (PT)