It is narrated from Hazrat Khursha (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: None of you should remain present with a murdered person (at the time he is being killed), because it is possible that he was killed while being oppressed, and those present there may also incur the displeasure of Allah.
Hadith Referenceمسند احمد / مسند الشاميين / 17522
Hadith Gradingحکم دارالسلام:إسناده ضعيف، ابن لهيعة سيئ الحفظ