لَا تَكْذِبْ
Do not lie.
This uses prohibitive lā with a jussive present verb; its primary force is to demand abstention. But رَبَّنَا لَا تُؤَاخِذْنَا
Our Lord, do not hold us accountable.
The grammatical shape is likewise prohibitive, yet the speaker's humble address to God makes its rhetorical purpose supplication. An adequate analysis names both grammatical form and contextual force.