Thus, there are two ways to determine the start and end of Ramaḍhān:

1. sighting the crescent on the 29th, or (if that's not possible) 2. completing the month as 30 days The evidence for this is the statement of the Prophet ﷺ: “Fast when you see it (the crescent of Ramaḍhān), and break your fast when you see it (the crescent of Shawwāl), and if the sky is overcast [and you cannot see the crescent on the 29th], calculate it (the months of Sha’bān and Shawwāl) as thirty days.” [Bukhāri & Muslim] 💡Benefit: Sheikh Ibn Bāz raḥimahullāh said: “Two just witnesses are required [to establish the sighting of the new moon] every month EXCEPT for the entry of Ramaḍhān, for it is sufficient to prove its entry by one just witness, according to the most correct of the two scholarly opinions; due to what is authentically reported from the authority of Ibn ’Umar raḍhiyallāhu ’anhu that he said: “People were looking out for the new moon, so I informed the Prophet ﷺ that I saw it, and he fasted and ordered the people to fast.” [Abū Dāwūd - graded 'Ṣaḥīḥ' by Sheikh Albāni in Irwā' Al-Ghalīl (4/16)] - [Majmū’ Fatāwā of Sheikh Ibn Bāz (15/64)]