I heard the Messenger of Allah ﷺ say, "His killer and the one who plunders him are in the Fire."Someone said to Amr, "But here you are fighting him."Amr replied, "He only said, 'His killer and the one who plunders him.'"
حدثنا عفان قال حدثنا حماد بن سلمة قال أخبرنا أبو حفص وكلثوم بن جبر عن أبي غادية قال قتل عمار بن ياسر فأخبر
سمعت رسول الله ﷺ يقول إن قاتله وسالبه في النار فقيل لعمرو فإنك هو ذا تقاتله قال إنما قال قاتله وسالبه
No references are available.
Its isnad is hasan, because of Kulthum bin Jabr, whom scholars accepted and relied upon. Abu Ghadiyah is Juhani, a companion, whose name was Yasar bin Sabi, and it is said that he was the killer of Ammar. Ibn Saad related the hadith (3/1/186), and Hakim graded it sahih (3/387), and Dhahabi agreed with him. Haythami said (7/244), "The men of Ahmad are trustworthy."