Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The preacher in a dream is a man who cries out of fear of God. Seeing him indicates salvation from hardships. Hearing his admonition indicates repentance.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
The preacher indicates a righteous man who calls to goodness. Whoever sees himself preach to people will gain high status.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The preacher is interpreted as relief. Whoever sees himself sit with one, his worry will disappear.