Sahih al-Bukhari 1987
Book 30: Fasting · Narrated by Alqama
Arabic
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ سُفْيَانَ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، قُلْتُ لِعَائِشَةَ ـ رضى الله عنها ـ هَلْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَخْتَصُّ مِنَ الأَيَّامِ شَيْئًا قَالَتْ لاَ، كَانَ عَمَلُهُ دِيمَةً، وَأَيُّكُمْ يُطِيقُ مَا كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُطِيقُ
English translation
Narrated Alqama:I asked `Aisha "Did Allah's Apostle, use to choose some special days (for fasting)?" She replied, "No, but he used to be regular (constant) (in his service of worshipping). Who amongst you can endure what Allah's Messenger (ﷺ) used to endure?
Reference: Sahih al-Bukhari 1987, Book of Fasting. English translation by Dr. Muhammad Muhsin Khan.