Reference: al-Fataawa as-Sa’diyyah – Page 136, Question 6
Question: What is your opinion regarding the khateeb using a microphone?
Response: My opinion is that there is no harm in doing so. And here, I wish to mention a beneficial point regarding this issue and other than it, and that is – issues which occurred after the (death of the) Prophet ﷺ are of two types: acts of worship and customs and habits.
As for acts of worship, then whoever practices an act of worship which Allaah nor His Messenger have legislated, then he is an innovator.
As for customs and habits, then the basic principle here is one of permissibility. So whoever renders a custom or habit impermissible, then he is required to bring his evidence; And if he brings forth evidence indicating its prohibition from the Book of Allaah, or from the Sunnah of the Messenger of Allaah, or from juristic reasoning based upon [authentic] legislation, then it will be rendered impermissible, otherwise the basic principle is one of permissibility.
And Shaykh al-Islaam Ibn Taymiyyah mentioned these two principles in “Iqtidaa as-Siraat al-Mustaqeem” and other than it from his books.
So these new appliances are to be treated from this perspective – and that is the basic principle is one of permissibility.
[Regarding] all permissible things – so long as they assist in that which is good, then they are good, and if they assist in that which is bad, then they are evil.