Musnad Ahmad Hadith 21092

It is narrated from Ubadah bin Samit (may Allah be pleased with him) with reference to Ubayy bin Ka'b (may Allah be pleased with him) that the Noble Prophet (peace and blessings of Allah be upon him) taught me a verse and taught the same verse to another man in a different way. I asked him, "Who taught you this verse?" He said, "The Noble Prophet (peace and blessings of Allah be upon him) taught me this verse." I swore and said, "The Noble Prophet (peace and blessings of Allah be upon him) taught me this verse in this way." And on that day, such doubts came to my mind regarding Islam as had never come before. I went to the service of the Noble Prophet (peace and blessings of Allah be upon him) and said, "O Messenger of Allah (peace and blessings of Allah be upon him), did you not teach me such and such verse in this way?" The Noble Prophet (peace and blessings of Allah be upon him) said, "Why not?" I said, "This person claims that you taught him the same verse in a different way." The Noble Prophet (peace and blessings of Allah be upon him) struck his hand on my chest, and all those doubts were removed, and after that, such doubts never came to me again. Then the Noble Prophet (peace and blessings of Allah be upon him) said, "Gabriel (peace be upon him) and Michael (peace be upon him) came to me. Gabriel (peace be upon him) said, 'Recite the Noble Qur'an on one letter.' Michael (peace be upon him) said, 'Ask them for an increase.' Gabriel (peace be upon him) said, 'Recite it on two letters.' Michael (peace be upon him) again said, 'Ask them for an increase,' until it reached seven letters." And he said, "Each of them is sufficient and healing."