Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
Flies in a dream are a weak, lowly, slandering man. Many flies indicate enemies or worry and grief. Killing them indicates comfort and healing.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
Flies indicate unlawful money. They may also indicate a man who gathers people for evil.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
Flies are interpreted as a weak enemy. Whoever sees one enter his stomach will mingle with a foolish man and gain wealth from him.