Is regret, repentance, and seeking forgiveness sufficient for my denouncement of a prophetic hadith, thinking it was the saying of a شيخ (sheikh), and am I thereby considered among the apostate mockers?

The hadith agreed upon as authentic, "If any of you feels drowsy during prayer, he should lie down until the sleep leaves him, for if one of you prays while drowsy, he might intend to seek forgiveness but instead curse himself," demonstrates the ease of Islamic law. The objection that arose in your mind, which you presumed to be the words of a shaykh and not those of the Prophet, peace and blessings be upon him, carries no blame for you. The sin is lifted from you because you did not intend to object to his words, peace and blessings be upon him, and because Allah has removed hardship from His servants concerning self-talk, error, and ignorance. We advise you to strive diligently in understanding the religion and to abandon obsessive doubts concerning matters of faith.