بِأَنَّ رَبَّكَ أَوْحَىٰ لَهَا
Because your Lord has directed it to do so. (99:5)
Bi-anna makes the causal relation explicit: the earth’s report occurs by divine direction. Rabbaka is the subject of anna, and the verbal clause awḥā lahā supplies its predicate. The pronoun in lahā refers to the earth.
The explanation does more than offer a mechanical account of an uncanny event. It relates the entire disclosure to divine command. This shows how an apparently brief causal phrase can carry a crucial part of a passage’s rhetorical argument.