It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him): "Take heed, the best people of the Ummah of Muhammad (peace and blessings be upon him) are those who watch the sun, the moon and the stars for the times of the prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1783