312. Upon sighting the crescent moon

اَللَّهُمَّ أَهْلِلْهُ عَلَيْنَا بِالْيُمْنِ وَالْإِيْمَانِ وَالسَّلَامَةِ وَالْإِسْلَامِ رَبِّيْ وَرَبُّكَ اللَّهُ

Allaahumma ahlilhu `alaina bil-yumni wal-iman, was-salamati wal-Islam, rabbi wa rabbuk Allah

Rasulullah (ﷺ) used to say this dua when he saw the new moon. It is masnun to recite this dua after seeing the new moon of Ramadan and all the months.