أَلَيْسَ اللَّهُ بِكَافٍ عَبْدَهُ / أَغَيْرَ اللَّهِ أَتَّخِذُ وَلِيًّا
Is Allah not sufficient for His servant? / Shall I take a protector other than Allah?
The first construction elicits acknowledgment of divine sufficiency. The second rejects taking another protector. Both use interrogative form, but they aim at opposite kinds of assent and repudiation.
A negative interrogative such as a-laysa is not automatically rhetorical negation. Context may make it a request to affirm a truth. Conversely, a-ghayra Allāh directs rejection toward a particular fronted complement.
AspectTaqrīrInkār
PurposeElicit acknowledgmentReject a claim or action
ExampleA-laysa Allāhu bi-kāfin ʿabdahuA-ghayra Allāhi attakhidhu waliyyan
EffectConfirm the truthRepudiate the false