Reference is made to the migration of 622 C.E. in an-Nawawi's Hadith
Answer Details
The migration referred to in an-Nawawi's Hadith is the Hijrah, which took place in 622 C.E. This was when Prophet Muhammad and his followers migrated from Mecca to Medina. The Hijrah marks the beginning of the Islamic calendar, hence it is often referred to in Islamic literature.