Whosoever wishes that his vision be truthful must seek to attain truthfulness, consume nothing but what is lawful, hold fast to the commandments and prohibitions. Furthermore, he should sleep in the state of ritual purity, face the Qibla and mention God until overtaken by sleep. The vision of such a one is seldom false. In addition, the most truthful of visions are those seen in the early morning [before dawn], as that is the time of divine descent, and proximity of mercy and forgiveness, respite from the devils. Its opposite is the vision seen in the early part of the night when the devils and devilish souls are spread about.
quoteswithmeaning.com