Does the supplication "O Allah, do not give the disbelievers a way over the believers" contradict Allah's saying, "And never will Allah grant to the disbelievers a way over the believers"? And was this supplication reported from the Salaf?

There is no objection to supplicating with the words: "O Allah, do not give the disbelievers a way over us," as it entails asking for steadfastness in faith so that the dominance of disbelievers, which occurs due to weakness of faith, may be prevented. This is not considered asking for the impossible, because even though Allah has promised believers that disbelievers will not dominate them, this promise is conditional upon fulfilling the reality of faith and its obligations. Supplication is a means to achieve what is sought, and whoever abandons obedience to Allah is punished by being deprived of this blessing. Thus, the supplication asks for the continuation of this divine protection for obedient believers.