Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "O people, learn knowledge, for none of you knows when people will come to need his (knowledge)." Then a man came to him and said: "O Abu Abd al-Rahman, what do you say about a man who recites the Qur'an backwards?" He said: "That is one whose heart is turned upside down." Then a copy of the Qur'an (mushaf) was brought to him which had been decorated and adorned with gold, and Abdullah (may Allah be pleased with him) said: "The best thing with which a mushaf can be adorned is its recitation in accordance with the truth."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8814