Imām Ibn al-Qayyim (d. 751 AH) said:

It is obligatory upon our faculties of hearing to: remain silent and listen to that which Allāh and His Messenger (صلى الله عليه وسلم) has made obligatory upon us. This is inclusive of listening to the meaning of Islām and īmān and both of their stipulations, listening to the recitation of the Qurʾān during the ṣalāh where the recitation is done loudly, listening attentively to the khuṭbah on Friday, according to that which is correct of the two opinions in this matter.

It is ḥarām to allow oneself to listen to disbelief and innovation except if, through listening to such things, one hopes for the attainment of the greater good.¹ This includes refuting their way, or testifying against those who have adopted misguidance, or for the purpose of increasing the strength of one’s īmān and adherence to the Sunnah by being acquainted with its opposite which takes the form of disbelief, innovation and its likeness.

Likewise, it is ḥarām to intentionally try to hear the secrets of others who try their utmost to hide them from you, hating that you should be acquainted with their private secrets. As long as those secrets do not concern one of the rights of Allāh which must be fulfilled, or cause harm to another Muslim which would necessitate the need to warn the companion of this secret and advise him.

Just as it is ḥarām to listen to the voices of women with whom there exists no familial relation if there is fear of fitnah in hearing them. Especially in situations where there is no need. True need may be in the form of seeking testimony, or essential communication, or seeking a legislative ruling, or judging between two parties, or seeking medical attention or the likes of such circumstances.

It is also ḥarām to allow ourselves to listen to the playing of stringed instruments, the instruments of music and idleness, like the lute, the mandolin or the reed. It is not obligatory for one to block his ears should he hear such sounds while he holds no desire to listen to it except if he fears that he may be enamoured by it, listening attentively to it as a result. If this is the case, then it is obligatory for him to block his ears such that he cannot hear it, as a way of blocking the means [to that which is ḥarām].

Endnotes: 

[1] Translator’s note: Listening to the people of innovation and disbelief for the purpose of refuting them is the occupation of the scholars. Shaykh al-Albānī said: “The people of innovation must not be refuted except by the person who has gained knowledge, both with regards to the sunnah and the innovation itself. I hope you recollect the ḥadīth of Ḥudhayfah ibn al-Yamān (رضي الله عنه) who said: ‘The people used to ask the Messenger of Allāh (صلى الله عليه وسلم) concerning goodness while I used to ask him concerning evil out of fear of falling into it.’ As the poet said: ‘I recognise evil not for evil’s sake, rather so I may protect myself from it. And whoever does not know goodness from evil will fall into it.’ Therefore, whoever is knowledgeable concerning good and evil like Ḥudhayfah ibn al-Yamān, knowledgeable of the sunnah to where he practises it himself and encourages others to do so, knowledgeable of innovation such that he is able to avoid it and warns others from it, this is the person who may debate the people of innovation or the innovators.
As for what some of our brothers have engaged in who have only learnt a little, then enter into debates with those stronger than them in knowledge, even if that knowledge is mixed and corrupted with all kinds of innovation, or philosophy; we advise these brothers to hold back and to stay away from the people of innovation, and not to try and debate them. This is because they will affect you with confusing, misunderstood matters…It is for this reason that there are many quotes from our pious predecessors like Mālik, Aḥmad, and others warning the people with severity from sitting with the people of innovation. Rather, they used to even order that the people cut themselves off from them out of fear that some of their confusions would sneak into their souls. See Jāmiʿ Turāth al-ʿAllāmah al-Albānī 8:423.

Source: al-Majmūʿ al-Qayyim: 162-163
Translated by: Riyāḍ al-Kanadī