Riyad as-Saliheen 1260
'Abdullah bin 'Amr bin Al-'As (May Allah be pleased with them) reported:
The Messenger of Allah ﷺ said, "Observing Saum (fasting) on three days of every month is equivalent to a full month's fasting."
[Al-Bukhari and Muslim].
وعن عبد الله بن عمرو بن العاص، رضي الله عنهما، قال: قال رسول الله:
"صوم ثلاثة أيام من كل شهر صوم الدهر كله" ((متفق عليه))
Classification
Sahih (Authentic)
References
Riyad as-Saliheen 1260
Riyad as-Saliheen Book of Virtues, Hadith 270