Fatimah bint al-Mundhir narrates from Asma bint Abi Bakr (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) "ordered the freeing of slaves at the time of an eclipse."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخسوف / 6366