Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī

ذِكْرُ تَفَضُّلِ اللَّهِ بِكِتْبَةِ صَائِمِي الْبِيضِ لَهُمْ أَجْرُ صَوْمِ الدَّهْرِ

ibnhibban:3651 – Abū Khalīfah > Abū al-Walīd al-Ṭayālisī > Shuʿbah > Anas b. Sīrīn > ʿAbd al-Malik b. al-Minhāl from his father

[Machine] He was with the Prophet (PBUH) and he said, "The Prophet (PBUH) used to command them to fast on Mondays and Thursdays and would say, 'It is the fasting of a lifetime.'"  

ابن حبّان:٣٦٥١ – أَخْبَرَنَا أَبُو خَلِيفَةَ حَدَّثَنَا أَبُو الْوَلِيدِ الطَّيَالِسِيُّ حَدَّثَنَا شُعْبَةُ حَدَّثَنِي أَنَسُ بْنُ سِيرِينَ سَمِعْتُ عَبْدَ الْمَلِكِ بْنَ الْمِنْهَالِ عَنْ أَبِيهِ

أَنَّهُ كَانَ مَعَ النَّبِيِّ ﷺ فَقَالَ كَانَ النَّبِيُّ ﷺ يَأْمُرُهُمْ بِصِيَامِ الْبِيضِ وَيَقُولُ «هِيَ صِيَامُ الدَّهْرِ»  

See similar narrations below:

Collected by Nasāʾī
nasai:2431 – Muḥammad b. Ḥātim > Ḥibbān > ʿAbdullāh > Shuʿbah > Anas b. Sīrīn > ʿAbd al-Malik b. Abū al-Minhāl from his father

the Prophet commanded them to fast the three days of Al-Bid. He said: "That is (equivalent to) fasting for the whole month."  

النسائي:٢٤٣١ – أَخْبَرَنَا مُحَمَّدُ بْنُ حَاتِمٍ قَالَ أَنْبَأَنَا حِبَّانُ قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ عَنْ شُعْبَةَ عَنْ أَنَسِ بْنِ سِيرِينَ قَالَ سَمِعْتُ عَبْدَ الْمَلِكِ بْنَ أَبِي الْمِنْهَالِ يُحَدِّثُ عَنْ أَبِيهِ

أَنَّ النَّبِيَّ ﷺ أَمَرَهُمْ بِصِيَامِ ثَلاَثَةِ أَيَّامِ الْبِيضِ قَالَ هِيَ صَوْمُ الشَّهْرِ