Man Lā Yaḥḍuruh al-Faqīh
Hadith 3421913 - وَ سَأَلَهُ سَمَاعَةُ : عَنِ اَلْيَوْمِ فِي شَهْرِ رَمَضَانَ يُخْتَلَفُ فِيهِ قَالَ «إِذَا اِجْتَمَعَ أَهْلُ اَلْمِصْرِ عَلَى صِيَامِهِ لِلرُّؤْيَةِ فَاقْضِهِ إِذَا كَانَ أَهْلُ اَلْمِصْرِ خَمْسَمِائَةِ إِنْسَانٍ.
Hadith.1913 - Sama'ah asked Imam (as) about a day in the Month of Ramadan over which there is a dispute.
Imam (as) said: "If the people of the city agree to fast based on sighting [the crescent], then observe it. This applies if the population of the city is five hundred people."