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
ahmad:21365 – Abū Kāmil > Ḥammād b. Salamah > Maʿbad b. Hilāl

[Machine] He said, "O Messenger of Allah, what is fasting?" He said, "It is a compensatory loan."  

أحمد:٢١٣٦٥ – حَدَّثَنَا أَبُو كَامِلٍ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ عَنْ مَعْبَدِ بْنِ هِلَالٍ حَدَّثَنِي رَجُلٌ فِي مَسْجِدِ دِمَشْقَ عَنْ عَوْفِ بْنِ مَالِكٍ عَنْ أَبِي ذَرٍّ

أَنَّهُ قَالَ يَا رَسُولَ اللهِ مَا الصَّوْمُ؟ قَالَ قَرْضٌ مُجْزِئٌ  

See similar narrations below:

Collected by Dārimī
darimi:1812 – Abū Nuʿaym > al-Aʿmash > Abū Ṣāliḥ > Abū Hurayrah

"The Messenger of Allah said: 'Fasting is a shield."' (Using translation from Nasāʾī 2224)  

الدارمي:١٨١٢ – أَخْبَرَنَا أَبُو نُعَيْمٍ حَدَّثَنَا الْأَعْمَشُ عَنْ أَبِي صَالِحٍ عَنْ أَبِي هُرَيْرَةَ قَالَ

قَالَ رَسُولُ اللَّهِ ﷺ «الصَّوْمُ جُنَّةٌ»