Bulugh al-Maram, Book 5, Hadith 675 (English) ⓘ

Ibn ’Umar (RAA) narrated, ‘The people were trying to sight the new moon (of Ramadan.) and when I reported to the Messenger of Allah that I had seen it, he fasted and commanded people to fast.’ Related by Abu Dawud, and Al-Hakim and Ibn Hibban graded it as Sahih.

وَعَنِ اِبْنِ عُمَرَ رَضِيَ اَللَّهُ عَنْهُمَا قَالَ: { تَرَاءَى اَلنَّاسُ اَلْهِلَالَ, فَأَخْبَرْتُ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-أَنِّي رَأَيْتُهُ, فَصَامَ, وَأَمَرَ اَلنَّاسَ بِصِيَامِهِ } رَوَاهُ أَبُو دَاوُدَ, وَصَحَّحَهُ اِبْنُ حِبَّانَ, وَالْحَاكِمُ 1‏.‏ ‏1 ‏- صحيح.‏ رواه أبو داود ( 2342 )‏، وابن حبان ( 3438 )‏، والحاكم ( 1 / 423 )‏.‏