(30) باب كَيْفَ الْفَجْرُ
Samurah said:
"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 reference: Book 22, Hadith 82
English translation: Vol. 3, Book 22, Hadith 2173