Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "Recite the Qur'an with correct inflection (i'rab), for it is in the Arabic language. Soon people will come who will try to straighten it, yet they will not be among the best of you."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8654