Ibn Abbas reported that the Prophet ﷺ gave Muhammad bin Maslama a sword and said, "Fight the polytheists as long as they are being fought. But when you see two swords clashing between Muslims, strike with your sword until it breaks, then sit in your house until a decreed death or a sinful hand reaches you."Abu Jamra said, "I then went to Ibn Umar, and he related to me the same account from the Prophet ﷺ."
عن ابن عباس: أن النبي ﷺ أعطى محمد بن مسلمة سيفا، فقال: قاتل المشركين ما قوتلوا، فإذا رأيت سيفين اختلفا بين المسلمين فاضرب حتى ينثلم، واقعد في بيتك حتى تأتيك منية قاضية، أو يد خاطئة. قال أبو جمرة: ثم أتيت ابن عمر فحذا لى على مثله عن النبي ﷺ.
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Tabarani related it in Al-Kabir (12/230) from Abbas bin Fadl Asfati, who said, Abu Walid Tayalisi narrated to us, who said, Thawab bin Utba narrated to us, from Abu Jamra, from Ibn Abbas, and he related it.Its chain is hasan because of Thawab bin Utba, for his hadith is hasan so long as he does not bring something that is rejected of him, and Abbas bin Fadl is truthful and his hadith is also hasan.