Who is the man who taught the Quran for 50 years in compliance with the words of the Messenger of Allah, peace and blessings be upon him: "The best among you are those who learn the Quran and teach it"?

Al-Bukhari reported a hadith from Uthman (may Allah be pleased with him), narrated by Abu Abd al-Rahman al-Sulami, who taught the Quran during Uthman's caliphate until the time of al-Hajjaj. Abu Abd al-Rahman al-Sulami sat for this long period, which could be up to seventy-two years or thirty-eight years. Therefore, the one referred to in the question is Abu Abd al-Rahman al-Sulami, because he taught the Quran for that long period, which is likely to have been fifty years.