In بِالْأَسْحَارِ, the prefix بِـ indicates a time relationship: “in the pre-dawn hours.” أَصْدَقُ الرُّؤْيَا is a comparison about dreams, not a claim about everything a person says.
For example, someone dreams near the end of the night. That identifies the time as sahar, but does not make every detail of the dream a certainty.
Dreams and waking evidence should be distinguished. Important decisions should rest on clear facts, reliable information, and sound consultation.