Hazrat Abu Bakr (RA) was the sole companion of the Prophet (PBUH) during the migration (Hijrah) to Medina in 622 CE. They hid in the Cave of Thawr for three days while Quraish searched for them. This companionship demonstrated Abu Bakr's unwavering faith and loyalty, earning him the title 'As-Siddiq' (the truthful).