Musannaf Ibn Abi Shaybah 9324 — What dawn is

Adi bin Thabit said: We disagreed about the dawn, so we came to Ibrahim and he said: "Dawn is of two kinds. One is the rising dawn (al-fajr al-sati'), which spreads lengthwise; it does not make the dawn prayer lawful nor food unlawful. The other is the red dawn that spreads across in breadth; it makes the prayer lawful and makes food and drink unlawful."