It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The Qur'an was revealed in seven ahruf (modes). So whoever recites according to one of them should not turn away from it to another out of aversion to it."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10235