Abu Bakra reported,

The Prophet ﷺ addressed us on the Day of Sacrifice. The narrator mentioned the hadith, and at the end of it he said, "Allah, bear witness. Let those present convey this to those who are absent, for many a one to whom a message is conveyed grasps it better than the one who heard it directly. Do not return to disbelief after me, striking the necks of one another."

Azami 6815

Sahih

عن أبي بكرة، قال

خطبنا النبي ﷺ يوم النحر، فذكر الحديث وفي آخره: قال: اللهم اشهد، فليبلغ الشاهد الغائب، فرب مبلغ أوعى من سامع، فلا ترجعوا بعدي كفارا، يضرب بعضكم رقاب بعض.

الأعظمي 6815صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Retaliation and crimes
Chapter
Prohibition of protected blood
Section
Killing a soul unjustly is among the greatest of major sins
Numbering
Jami al-Kamil 6815 (2nd edition)
Azami 6815