Answer
(Fatwa: 764/752 =D/1429)
The purpose of going into Tablighi Jamah is to meet other people and learn and teach together. And those, who have no knowledge or have little knowledge as well as do not take care in carrying out religious acts, reform themselves while keeping a company with the learned people, acting upon the Shariah; they strengthen their faith and pledge to do good deeds and keep away from evil things and then return back home. Therefore, it is not necessary that a person should leave first all wrongdoings and then go to Jamah. Many people involved in unlawful activities go to Jamah and there they feel evils in them. It creates strength in their faith so they gradually start forsaking bad deeds.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband