Allah knows best about what they were doing. (Using translation from Abū Dāʾūd 4711)

أَنَّ النَّبِيَّ ﷺ سُئِلَ عَنْ ذَرَارِيِّ الْمُشْرِكِينَ فَقَالَ اللهُ أَعْلَمُ بِمَا كَانُوا عَامِلِينَ