Sunan Ibn Majah, Book 7, Hadith 1811 (In-Book) ⓘ
It was narrated from Rabi’ah bin Ghaz that he asked ‘Aishah about the fasting of the Messenger of Allah. She said: “He used to make sure he fasted on Mondays and Thursdays.”
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا يَحْيَى بْنُ حَمْزَةَ، حَدَّثَنِي ثَوْرُ بْنُ يَزِيدَ، عَنْ خَالِدِ بْنِ مَعْدَانَ، عَنْ رَبِيعَةَ بْنِ الْغَازِ، أَنَّهُ سَأَلَ عَائِشَةَ عَنْ صِيَامِ، رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ فَقَالَتْ كَانَ يَتَحَرَّى صِيَامَ الاِثْنَيْنِ وَالْخَمِيسِ .
also referenced under: Hadith 1739 (Reference) & Volume 2, Book 7, Hadith 1739 (DarusSalam)