"Do not fast ahead of the month, except for a man who habitually fasts, and that day happenes to be one of his regular fasts." '
Sunan an-Nasa'i Book 22, Hadith 83
← Previous Hadith "The Messenger of Allah said; 'DO not be confused by the Adhan of Bilal, or by this whiteness, until dawn appears like this" - meaning horizontally. (One of the narrators) Abu Dawud said: "And he spread out his hands gesturing to the right and left."

Sunan an-Nasa'i Book 22, Hadith 82 Next Hadith → "None should fast one or two days ahead of the month except, someone who had a prior habit for fasting, in which case let him fast." '

Sunan an-Nasa'i Book 22, Hadith 84