The evidence that the day when the crescent is obscured falls under this prohibition is the report of Ibn ‘Abbās, traced back to the Prophet: “Do not fast before Ramadan. Begin fasting upon sighting the crescent, and end the fast upon sighting it. If a cloud or haze obscures it, complete thirty days.” Ibn Hibbān included it in his Sahīh (1). This explicitly establishes that fasting on the day when the crescent is obscured, without sighting it or completing thirty days, is fasting before Ramadan.
He said: “Do not begin fasting ahead of the month unless you sight the crescent or complete the count, and do not end the fast until you sight the crescent or complete the count” (2).
He said: “Begin fasting upon sighting the crescent, and end the fast upon sighting it. If clouds come between you and it, complete the count of thirty days, and do not fast in anticipation of the month” (3). Al-Tirmidhī (4) said: “It is an authentic hadith” (5).
In al-Nasā’ī (6), a report is transmitted by [Abū] Yūnus, from Simāk, from ‘Ikrima, from Ibn ‘Abbās, who traced it back to the Prophet: “Begin fasting upon sighting the crescent, and end the fast upon sighting it (7). If there comes (8) between you and it