What is the ruling on one who strove to form an independent judgment (ijtihad) on a Sharia matter and erred therein, and how should he be dealt with? Is it permissible to pray behind him? And is he considered a hypocrite if his error is explained to him and he does not retract it?

If the issue is one that allows for ijtihad (independent reasoning), and the person is qualified for ijtihad, then they are rewarded for it even if they err in the matter itself. Disagreement in such issues does not necessitate enmity or discord, nor does it negate one's integrity. It is not permissible to describe a mujtahid (one who performs ijtihad) as a hypocrite. However, if the issue does not permit disagreement, or if the person is not qualified for ijtihad, then they are mistaken and should be advised. Praying behind such a person is permissible as long as they have not committed an act of disbelief that takes them out of the fold of Islam. One must be cautious about describing a Muslim as a hypocrite or being hasty in accusing them of wickedness or innovation.