Concept:The Cave of Thawr is linked to the Prophet's migration from Makkah to Madinah.Explanation:During the Hijrah, the Prophet Muhammad (S.A.W) and Abu Bakr (R.A) left Makkah secretly.They hid inside the Cave of Thawr for three days to avoid the Quraysh pursuers.This event is specifically associated with the migration, not revelation, sermon, or Hajarah's hardship.Answer:B. migration from Makkah to Madinah