وَلَا تَثْبُتُ قَدَمُ الْإِسْلَامِ إِلَّا عَلَى ظَهْرِ التَّسْلِيمِ وَالِاسْتِسْلَامِ
One’s footing in Islam is established through acceptance and surrender.
Clause structure: Lā tathbutu ... illā ʿalā restricts the condition for firmness. ʿAlā ẓahr al-taslīm wa-l-istislām is figurative, not a claim about a physical back.
Meaning and inference: Firm adherence depends on submission to what is established from Allah and His Messenger.
Limit of inference: Submission does not require abandoning understanding; it requires not rejecting established guidance without sound grounds.