Ja'far bin Muhammad narrated from his father, who narrated from his grandfather, who said that a book was found attached to the hilt of the sword of the Messenger of Allah ﷺ, stating: "Indeed, among the people, the greatest wrongdoer in the sight of Allah, the Exalted and Glorious, is the killer who kills one who does not fight, and who kills someone other than his own killer. And whoever takes as his guardian anyone other than his own masters has indeed denied the revelation which Allah, the Exalted, sent down upon Muhammad ﷺ."
Hadith Referenceمسند الإمام الشافعي / كتاب القتل والقصاص والديات والقسامة / 1618
Hadith Takhrijاسناده ضعيف لضعف شيخ الشافعي و لانقطاعه واخرجه البيهقي: 8 / 26 - وفي المعرفة السنن والآثار له (4797) - وعبد الرزاق (18847)۔ وابو یعلی (330)۔
Muhammad bin Ishaq narrated that I asked Abu Ja'far Muhammad bin Ali, "What was in the scroll that was in the sheath of the Messenger of Allah’s ﷺ sword?" He replied: "It contained that Allah has cursed the one who kills someone other than his killer, and has also cursed the one who strikes someone other than his striker. And whoever gives someone’s blessing to a non-guardian as an owner, he has denied the revelation that Allah Almighty sent down upon Muhammad ﷺ."
Hadith Referenceمسند الإمام الشافعي / كتاب القتل والقصاص والديات والقسامة / 1619
Hadith Takhrijاسناده ضعيف لإعضاله اخرجه البيهقي: 26/8 - وفى المعرفة السنن والآثار له (4798)۔