Salama bin Akwa reported,

We set out with the Prophet ﷺ toward Khaybar, traveling by night.He then mentioned part of the story of Khaybar, and said, "When the two sides drew up in ranks, Amir's sword was short. He reached out with it to strike at a Jew's leg, but the blade rebounded and struck the inside of Amir's own knee, and he died from it."He continued, "When they returned, the Messenger of Allah ﷺ saw me and took my hand."He asked, "What is the matter with you?"I said to him, "May my father and mother be ransomed for you, people are claiming that Amir's deeds have been rendered worthless."The Prophet ﷺ said, "Whoever said that has lied. He has two rewards," and he held two of his fingers together. "He was a striver, a warrior. Few Arabs have walked the earth like him."

Azami 7912

Sahih

عن سلمة بن الأكوع قال

خرجنا مع النبي ﷺ إلى خيبر، فسرنا ليلا، - فذكر بعض قصة خيبر- ثم قال: فلما تصاف القوم كان سيف عامر قصيرا، فتناول به ساق يهودي، ليضربه، ويرجع ذباب سيفه، فأصاب عين ركبة عامر فمات منه، قال: فلما قفلوا قال سلمة: رآني رسول الله ﷺ وهو آخذ بيدي، قال: ما لك؟ قلت له: فداك أبي وأمي زعموا أن عامرا حبط عمله، قال النبي ﷺ: كذب من قاله، إن له لأجرين، وجمع بين إصبعيه، إنه لجاهد مجاهد، قل عربي مشى بها مثله.

الأعظمي 7912صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Jihad
Chapter
Rulings on jihad and its etiquette
Section
One who fought in the cause of Allah and his sword struck back and killed him
Numbering
Jami al-Kamil 7912 (2nd edition)
Azami 7912