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
nasai-kubra:2543 – ʿAbdullāh b. Muḥammad al-Ḍaʿyf > Yaʿqūb > Shuʿbah > Muḥammad b. ʿAbdullāh b. Abū Yaʿqūb > Abū Naṣr > Rajāʾ b. Ḥaywah > Abū Umāmah al-Bāhilī

"Which deed is best?" he said: "Take to fasting, for there is nothing equal to it." (Using translation from Nasāʾī 2222)  

الكبرى للنسائي:٢٥٤٣ – أَخْبَرَنَا عَبْدُ اللهِ بْنُ مُحَمَّدٍ الضَّعيفُ قَالَ حَدَّثَنَا يَعْقُوبُ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ مُحَمَّدِ بْنِ عَبْدِ اللهِ بْنِ أَبِي يَعْقُوبَ عَنْ أَبِي نَصْرٍ عَنْ رَجَاءِ بْنِ حَيْوَةَ عَنْ أَبِي أُمَامَةَ الْبَاهِلِيِّ

أَنَّهُ سَأَلَ النَّبِيَّ ﷺ أَيُّ الْعَمَلِ أَفْضَلُ؟ قَالَ «عَلَيْكَ بِالصَّوْمِ فَإِنَّهُ لَا عِدْلَ لَهُ»  

See similar narrations below:

Collected by Nasāʾī, Suyūṭī
nasai:2222 – ʿAbdullāh b. Muḥammad al-Ḍaʿīf Shaykh Ṣāliḥ And al-Ḍḍaʿīf Laqab Likathrah ʿIbādatih > Yaʿqūb al-Ḥaḍramī > Shuʿbah > Muḥammad b. ʿAbdullāh b. Abū Yaʿqūb > Abū Naṣr > Rajāʾ b. Ḥaywah > Abū Umāmah

"Which deed is best?" he said: "Take to fasting, for there is nothing equal to it."  

النسائي:٢٢٢٢ – أَخْبَرَنِي عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ الضَّعِيفُ شَيْخٌ صَالِحٌ وَالضَّعِيفُ لَقَبٌ لِكَثْرَةِ عِبَادَتِهِ قَالَ أَخْبَرَنَا يَعْقُوبُ الْحَضْرَمِيُّ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ مُحَمَّدِ بْنِ عَبْدِ اللَّهِ بْنِ أَبِي يَعْقُوبَ عَنْ أَبِي نَصْرٍ عَنْ رَجَاءِ بْنِ حَيْوَةَ عَنْ أَبِي أُمَامَةَ

أَنَّهُ سَأَلَ رَسُولَ اللَّهِ ﷺ أَىُّ الْعَمَلِ أَفْضَلُ قَالَ عَلَيْكَ بِالصَّوْمِ فَإِنَّهُ لاَ عِدْلَ لَهُ