Sayyiduna Abu Mas'ud al-Ansari (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "The sun and the moon are two of the signs of Allah; through them Allah, the Lord of Might, frightens His servants. They do not lose their light because of anyone's death or life. When you see anything of this, then pray and supplicate until they become bright again."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخسوف / 6353