[ Assalamu Alaikum WaRahmatullahi WaBarakatuhu]
A chief principle of Dawah and Tableegh in Islam is 'nafeer', that is, leaving one's native place and going to the places which afford oppurtunities of acquiring deen and then coming back to fellow tribesmen and nationals for disseminating among them the religious knowledge thus acquired. The following verse of surah Nisaa which was revealed on the Occasion of the Battle of Uhud:
Oh you who have attained to faith! be fully prepared against danger, wether you go to war in small groups or all together.
contains instructions though for war time strategy, yet its general scope includes any nafeer made for the cause of deen. Qazi Bezaavi rahmatullah alaih has also given this interpretation amongst others in his commentary of the holy Quran. In Surah Taubah, there is a particular verse of this idiom:
It is not desirable that all of the believers take the field (in time of war). from within every group in their midst, some shall refrain from going forth to war, and shall devote themselves instead to acquiring a deeper knowledge of the faith, and thus be able to, teach their homecoming brethren, so that these too, might guard themselves against evil.
During the time of the holy Prophet sallallahu alaihi wa sallam, deputations from different tribes came to medinah to acquire the knowledge and practice of deen. Staying for a period of 7 to 10 days ( a few stayed for around 3 weeks and so forth) and having got the basic knowledge of deen, these groups went back to their homes to acquaint the people of their community with Deen.
(Shaikh Maulana Muhammad Ilyas rahmatullah alaih)
Wa alaikum assalam wa rahmatullahi wa barakatuhu