Hadith.5325 - Ibn Abi Umayr narrated from some of his companions from Abu Abdullah (as) regarding a Muslim man who was in the land of the disbelievers and was mistakenly killed by the Muslims. Later, the Imam became aware of it.
Imam (as) said
"A believing slave must be freed in his place, and this is in accordance with the saying of Allah (swt), the Mighty and Majestic:
'But if he belonged to a people hostile to you and he was a believer, then the freeing of a believing slave [is required]' (Surah An-Nisa 4:92).