Musical instruments is a general term encompassing all instruments of music. There is, however, one exception to this general ruling: the use of the duff on special occasions. The sunnah has permitted it, such as its use at weddings, on the days of Eid, and upon the arrival of an eminent absent person—one holding authority or the like. All of this is established in the sunnah.
As for the first, it is clear, for the Messenger of Allah, peace and blessings be upon him, said: “Publicize the marriage, and beat the duff for it.” (1) Although there is some weakness in this hadith, it is supported by corroborating reports.
As for the Eids, Abu Bakr al-Siddiq, may Allah be pleased with him, saw two young girls singing and beating the duff in the presence of the Prophet, peace and blessings be upon him. He rebuked them, saying, “The flute of Satan in the presence of the Messenger of Allah, peace and blessings be upon him?!” He replied, “Leave them, for these are days of Eid.” (2)
As for the arrival of an absent person, the Prophet, peace and blessings be upon him, returned from a journey, and a woman came to him and said, “O Messenger of Allah, I had vowed that, if Allah returned you safely, I would beat the duff before you.” The Messenger of Allah, peace and blessings be upon him, said to her, “Fulfil your vow.” (3)