How can I ask God for a vision to clarify a matter?

There is no harm for a Muslim to ask Allah to show him a dream that clarifies a matter, but he should not be certain of the dream's truthfulness, as it might be a self-revelation or a manipulation from Satan. It is more complete for a Muslim to supplicate with comprehensive prayers and to humbly implore Allah to facilitate goodness for him. Among what is legislated when in doubt is the الاستخارة (istikharah) prayer.