We were indeed commanded to free slaves during the eclipse prayer.
حدثنا عثام بن علي أبو علي العامري قال حدثنا هشام بن عروة عن فاطمة
إن كنا لنؤمر بالعتاقة في صلاة الخسوف
No references are available.
Its isnad is sahih. Bukhari narrated it (2/543, no. 1054) in the chapter on the eclipse, Abu Dawud (1/310, no. 1192) in the chapter on the prayer for rain, Darimi (1/432, no. 1532), and Ibn Khuzayma (2/329, no. 1401). Hakim graded it sahih (1/331) according to the criterion of the two sheikhs, and Dhahabi remained silent on it.