Musnad Ahmad Hadith 21132

It is narrated from Ubadah (may Allah be pleased with him) with reference to Ubayy bin Ka'b (may Allah be pleased with him) that the Noble Prophet (ﷺ) 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 replied, "The Noble Prophet (ﷺ) taught me this verse." I swore and said, "The Noble Prophet (ﷺ) taught me this verse in this way." And on that day, the doubts that came to my mind regarding Islam had never come before. I went to the service of the Noble Prophet (ﷺ) and said, "O Messenger of Allah (ﷺ), did you not teach me such and such verse in this way?" The Noble Prophet (ﷺ) said, "Why not?" I said, "This person claims that you taught him the same verse in a different way." The Noble Prophet (ﷺ) struck his hand on my chest, which removed all those doubts, and after that, such doubts never came to me again. Then the Noble Prophet (ﷺ) said, "Jibreel (peace be upon him) and Mika'il (peace be upon him) came to me. Jibreel (peace be upon him) said, 'Recite the Noble Qur'an on one letter.' Mika'il (peace be upon him) said, 'Ask them for an increase.' Jibreel (peace be upon him) said, 'Recite it on two letters.' Mika'il (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.'"