Musnad Ahmad 26:295

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Abd al-Rahman ibn ‘Abis, who said: A man from Hamdan—one of the companions of ‘Abdullah, though he did not name him to us—narrated to us, saying: When ‘Abdullah intended to go to Medina, he gathered his companions and said: "By Allah, I truly hope that there has become among you today some of the best of what has become among the armies of the Muslims in terms of religion, jurisprudence, and knowledge of the Quran. Indeed, this Quran was revealed in [different] dialects. By Allah, if two men were to dispute—the most intensely they have ever disputed over anything—and then one reciter said, 'This is how I was taught to recite,' he would say, 'You have done well.' And if the other said [the same], he would say, 'Both of you are doing well.' So recite: 'Indeed, truthfulness leads to righteousness, and righteousness leads to Paradise; and indeed, lying leads to wickedness, and wickedness leads to the Fire.' Consider that by the saying of one of you to his companion: 'You lied and acted wickedly,' and by his saying when he confirms him: 'You spoke the truth and acted righteously.' Indeed, this Quran does not differ, nor does it become worn out, nor does it become trivialized by frequent repetition. So whoever recites it in one dialect, let him not abandon it out of aversion to it; and whoever recites it in any of those dialects which the Messenger of Allah (peace and blessings of Allah be upon him) taught, let him not abandon it out of aversion to it. For whoever denies one verse of it, denies it all. It is merely like the saying of one of you to his companion: 'Hurry' and 'Come here.' By Allah, if I knew of a man more knowledgeable than I regarding what Allah revealed to Muhammad (peace and blessings of Allah be upon him), I would seek him out until I added his knowledge to my own. There will be people who cause the prayer to die; so perform the prayer at its time, and make your prayer with them a voluntary act. Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) used to be presented with the Quran [for review] every Ramadan, and in the year he passed away, I presented it twice. He informed me that I was doing well, and I have recited seventy surahs from the mouth of the Messenger of Allah (peace and blessings of Allah be upon him)."