These are the words of someone who fully understood singing and its effects, for no one regularly sings or listens to song except that his heart falls into (nifaq) Hypocrisy without him realizing. If such a person understood the reality of nifaq and its end he would see it in his own heart. Never do the love of song and the love of Qur`an come together in a person’s heart except that one expels the other. I and others have witnessed how heavy the Qur`an feels to singers and song-listeners; how they coil when it is recited and how they get angry with a reciter when he recites too long for them (in prayer etc); and how their hearts do not benefit from what he recites: they are not moved to do anything by it. But when the Qur`an of Shaytân comes, la ilaha illallah! How they lower their voices and settle down! How their hearts feel at peace and how the crying and emotions start, how moved they are inwardly and outwardly and spend on clothing and perfume and staying up hoping for a long night ahead. If this is not nifaq then it is certainly the way to it and its foundation.
Ibn Al-Qayyim (rahimahullah) [Madaarij Al-Saalikeen] (via byyourmercyallah)