Qatadah bin Milhan (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) directed us to observe Saum (fasting) on the thirteenth, fourteenth and fifteenth of the (lunar) month.[Abu Dawud]. (ES)
App reference (ES): Book 9, Hadith 273 (ES)
Arabic/English book reference (ES): Book 9, Hadith 1263 (ES)