“The Islamic Ruling On Music And Singing In Light Of The Quraan, The Sunnah, And The Consensus Of Our Pious Predecessors,” by Abu Bilal Mustafa Al-Kanadi, is a detailed discourse on this topic. The ‘duff’ (tambourine), a percussion instrument, is allowed as an exception to the general prohibition on musical instruments. This is proved by numerous instances of Rasul Allah’s taqriri Sunnah (i.e. he saw its use but did not forbid it.)
The duff, accompanied by song, was used in the Prophet’s time on special occasions and weddings, but not as a general pastime.

A hadith narrated by Imam Bukhari, on the prohibition of musical instruments is: “From among my followers there will be some people who will consider illegal sexual intercourse, the wearing of silk (by men), the drinking of alcoholic drinks and the use of musical instruments, as lawful…. Allah will destroy them during the night and will let the mountain fall on them, and He will transform the rest of them into monkeys and pigs and they will remain so till the Day of Resurrection.” [Sahih Bukhari]

Singing is not forbidden, provided that the content is appropriate. However, singing to the accompaniment of musical instruments becomes forbidden because of the haraam (forbidden) element of music. We see a large part of the Ummah being deceived about life and morality, wasting the precious little time they have of this life, while engrossed in musical ‘entertainment.’
The obsession with music has become as common as the air we breathe. The seriousness of this sin can be judged by the following hadith of Prophet Muhammad (sal Allahu alaihi wa sallam), on the authority of Anas (radi Allahu anhu):

“On the Day of Resurrection, Allah will pour molten lead into the ears of whoever sits listening to a songstress.” [Ibn Asakir in Tareekha]