Sunan an-Nasa'i 2400
سنن النسائي#2400SahihIt was narrated that 'Abdullah bin 'Amr said:"The Messenger of Allah said to me: 'Read the Qur'an in a month.' I said: 'I am able to do more than that. ' And I kept asking him until he said: 'In five days.' And he said: 'Fast three days a month.' I said: 'I am able to do more than that.' And 'Observe thhe most beloved of fasting to Allah, the Mighty and Sublime, the fast one day and not the next." (Suahih)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih Isnaad
Al-AlbaniSahih Isnaad
Zubair Ali ZaiHasan
In-book reference: 22:311