Yahya bin al-Jazzar says that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) was asked about a man who ate sahur thinking it was still night while dawn had already broken. He said: Whoever ate at the beginning of the day, let him eat at its end too.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8007