What is the jurisprudential ruling, with evidence from the authentic Sunnah and exegeses, on the fasting of one who only begins fasting upon seeing light in the sky, and only breaks their fast after night completely covers the sky, based on verse 187 of Surat Al-Baqarah: "until the white thread becomes distinct to you from the black thread of dawn. Then complete the fast until night"?

The starting point of the fast is the true dawn (al-fajr al-sadiq), based on the Almighty's saying: "And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]." The Prophet, peace and blessings be upon him, clarified this as the whiteness of day and the blackness of night. As for the time the fast ends, it is at sunset and the onset of night, based on the Almighty's saying: "Then complete the fast until the night." One should hasten to break the fast upon verifying the sunset, and it is not legislated to delay it.