There are two aspects of Tabligh. One is to convey the Deen of Allah. That is the responsibility of every Muslim. He has to convey the Deen of Allah to the best of his ability, to his family, friends, Muslim and non-Muslims.
The second aspect of Tabligh is going out in a group of people for a specific number of days, three days, forty days, four months, etc. According to Shari?ah, there is no instruction or prohibition either to do Tabligh in this way. Such a procedure of Tabligh is Mubaah (permissible) if one does not regard it as compulsory and does not do anything un-Islamic in this procedure.
It must be pointed out that this method is tried and tested. It is effective and became a means of guidance for many people from all around the world. The procedure should be viewed in light of any other procedural aspects which have been tried, tested and proven effective. It gains the attention and support of people.
and Allah Ta’ala Knows Best
Mu