Abu Ubaydah bin Abdullah bin Mas'ud said: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) used to pray Maghrib when the edge of the sun had set, then he would swear that this is the time about which Allah Almighty said: "Establish the prayer at the decline of the sun" [Surah al-Isra: 78].
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9095