"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."
Reference: Sunan an-Nasa'i 2171 In-book : Book 22, Hadith 82 English translation : Vol. 3, Book 22, Hadith 2173
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