Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The mihrab in a dream indicates the Imam of the Muslims or their leader. It is a place of obedience and worship. Praying in it indicates good religion and the glad tidings of a righteous son.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
The mihrab indicates a righteous wife or authority. Whoever sees himself praying in a mihrab will be blessed with a blessed baby boy.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The mihrab is interpreted as a righteous man. Entering it indicates security and guidance. Whoever sees himself building a mihrab is establishing a righteous work.