Waail bin Hajar reported,

The Prophet ﷺ was brought a killer, being led by the guardian of the slain man with a leather strap.The Messenger of Allah ﷺ asked the guardian of the slain man, "Will you pardon him?"He said, "No."The Prophet ﷺ asked, "Will you accept the blood money?"He said, "No."The Prophet ﷺ asked, "Then will you kill him?"He said, "Yes."The Prophet ﷺ said, "Take him away."When he had taken him away and turned from where the Prophet ﷺ was, the Prophet ﷺ called him back and asked him, "Will you pardon him?"He said, "No."The Prophet ﷺ asked, "Will you accept the blood money?"He said, "No."The Prophet ﷺ asked, "Then will you kill him?"He said, "Yes."The Prophet ﷺ said, "Take him away."At that point the Messenger of Allah ﷺ said, "Understand this, if you pardon him, he will bear his own sin and the sin of your companion."So he pardoned him and let him go. And I saw the man dragging his leather strap behind him.Yahya said, "This version is the better of the two."

Nasai 4729

Sahih

أخبرنا محمد بن بشار قال حدثنا يحيى قال حدثنا جامع بن مطر الحبطي عن علقمة بن وائل عن أبيه عن النبي ﷺ بمثله قال يحيى وهو أحسن منه

النسائي 4729صحيح
Contents
Reference
Commentary
Ayat
Collection
Sunan Nasai Sughra
Book
Sworn testimony
Chapter
Disagreement among narrators of the hadith of Alqama bin Waail regarding this
Numbering
Darussalam 4729
Nasai 4729