The Crescent, New Moon sighting
عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ وَ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ جَمِيعاً عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ حَمَّادِ بْنِ عُثْمَانَ عَنِ الْحَلَبِيِّ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ إِنَّهُ سُئِلَ عَنِ الْأَهِلَّةِ فَقَالَ هِيَ أَهِلَّةُ الشُّهُورِ فَإِذَا رَأَيْتَ الْهِلَالِ فَصُمْ وَ إِذَا رَأَيْتَهُ فَأَفْطِرْ
Ali Bin Ibrahim, from his father, and Muhammad Bin Yahya, from Ahmad Bin Muhammad, altogether from Ibn Abu Umeyr, from Hammad Bin Usman, from Al Halby,
(It has been narrated) from Abu Abdullah-asws, having been asked about the crescent, so he-asws said: ‘It is the crescent of the month. So whenever you see the new moon, so Fast, and when you see it (again), so break the Fasting,’ (as month of Shawwal starts).[1]
NB: Moonsighting for the 1st 2nd and the 3rd of the month | Hubeali.com
[1] Al Kafi – V 4 – The Book of Fasts Ch 6 H 1