Sunan Ibn Majah 1708
سنن ابن ماجه#1708Da'ifIt was narrated from Abu Dharr that the Messenger of Allah (ﷺ) said:“Whoever fasts three days in every month, that is fasting for a lifetime.” Then, in testimony of that, Allah revealed: “Whoever brings a good deed shall have ten time the like thereof to his credit.” [6:160] So one day is equivalent to ten (in reward)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiDaif
In-book reference: 7:71