A conditional sentence can combine different ending groups.
إِنْ تَنْصُرُوا اللَّهَ يَنْصُرْكُمْ
If you support Allah's cause, He will help you.
Condition verb: تَنْصُرُوا — its inflectional nun is removed.
Answer verb: يَنْصُرْكُمْ — its final dammah becomes sukun.
إِنْ تَرْحَمْ تُرْحَمْ
If you show mercy, you will be shown mercy. Both verbs end in jussive sukun; the second is passive.