مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2222
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn 'Abbas (رضي الله عنه) that The Messenger of Allah (ﷺ) set free whoever came out to him of slaves.
Musnad Ahmad 2229Hasan because of corroborating evidence; this is a da'eef]