What was the number of Muslims before the Hijra, and what were the reasons for their decline in number in Mecca and their increase in Medina?

The number of Muslims before the Hijrah was not specified, but it was small due to the persecution they faced from Quraish in Mecca. After the Muslims migrated to Medina, their numbers increased, and the Ansar embraced Islam, making Medina the abode of Islam and granting Muslims strength, as Allah Almighty stated: "And remember when you were few and oppressed in the land, fearing that people might abduct you, but He sheltered you and supported you with His victory and provided you with good things that you might be grateful." (Al-Anfal: 26).