Conventional banks or associations are based on interest economy. The exchange of interest is the main work of these banks or associations. In the present capitalist economy, these banks are the main means of propagating and spreading interest. And the person on duty in the bank or association is directly involved in the interest business in various ways. Just as it is haraam to give and take interest, so it is haraam to be involved in the usury of others. Allah's Messenger (peace and blessings of Allah be upon him) did not only curse the usurer and the receiver ; Rather, it has cursed its author (ie, the accountant of interest) and its witnesses. Hazrat Jabir Ra. He said , "The Messenger of Allah, may Allah bless him and grant him peace, cursed the usurer and the usurer, and the usurer and the witness." -Sahih Muslim , Hadith 1598 So it is not lawful for a Muslim to work in a conventional bank or association and to enjoy its salary. As it is interest based, it is haraam to open general savings accounts or savings accounts for different periods or to take any kind of loan on interest basis in these banks or associations. If someone opens such an account, it should be closed immediately and the interest received from it should be given in charity without the intention of reward. However, in case of need, it is permissible to open a current account in the bank , make interest free transactions like TT , pay-order etc. - Qurtubi 3/225 in Tafseer (Surah Baqara: 265) ; Takmila Fathul Mulhim 1/219 The one who is directly involved in usury is "Fasek" meaning sinner , and praying behind Fasek is close to Makrooh Tahrimi meaning Haram. Therefore, if there is no irrefutable problem, it is necessary to avoid praying behind such an Imam. Among the famous books of Hanafi school is 'Fataawa-e-Shami ' : Fatawa Shami-1/560. 3 More See books like Ahsanul Fatawa-3/209 , Imdadul Fatawa-1/411 , Gunia-480 etc.