Abd al-Rahman bin Yazid narrated: We were with Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) on the road to Makkah, and when the sun set he said: "This is the darkness of the night (ghasaq al-layl)." Then the adhan was called, then he said: "By Allah, besides whom there is no god, this is the time of this prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9108