ENOfficial
Abu Qatada Ansari (Allah be pleased with him) reported that Allah's Massenger (ﷺ) was asked about fasting on Monday, whereupon he said: It is (the day) when I was born and revelation was sent down to me.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا مَهْدِيُّ بْنُ مَيْمُونٍ، عَنْ غَيْلاَنَ، عَنْ عَبْدِ اللَّهِ بْنِ مَعْبَدٍ الزِّمَّانِيِّ، عَنْ أَبِي قَتَادَةَ الأَنْصَارِيِّ، رضى الله عنه أَنَّرَسُولَ اللَّهِ صلى الله عليه وسلم سُئِلَ عَنْ صَوْمِ الاِثْنَيْنِ فَقَالَ " فِيهِ وُلِدْتُ وَفِيهِ أُنْزِلَ عَلَىَّ " .
sunnah.com