The mihrab before the qibla change.

When the Prophet Muhammad migrated to Medina, Muslims prayed towards the Al-Aqsa Mosque in Jerusalem for about 16-17 months. During this time, the Prophet carried the desire to face the Kaaba in his heart and awaited revelation from Allah regarding this matter. In February 624 AD, the 144th verse of Surah Al-Baqarah was revealed, and the qibla was turned towards the Kaaba. Upon this, the Prophet turned his direction towards the Kaaba; the congregation also turned with him. This historical turning point of the qibla change gave rise to two different mihrabs within the Prophet's Mosque: the first being the old mihrab facing Jerusalem (this point), and the second being the main mihrab facing the Kaaba, which is still in use today. The old mihrab has been marked with a special sign in later periods. [Source: "Qibla", TDV Islamic Encyclopedia, https://islamansiklopedisi.org.tr/kible; Bukhari, "Salat", 31]