Sahl bin Saad reported,

They did not count from the Prophet's ﷺ commissioning, nor from his death. They counted only from his arrival in Medina.

Bukhari 3934

Sahih

حدثنا عبد الله بن مسلمة حدثنا عبد العزيز عن أبيه

عن سهل بن سعد قال

ما عدوا من مبعث النبي ﷺ ولا من وفاته ما عدوا إلا من مقدمه المدينة

البخاري 3934صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Virtues of the Ansar
Chapter
History, from where they dated history
Numbering
Darussalam 3934
Bukhari 3934