All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The saved sect is the one that Allaah the Almighty saved from disagreement over fundamental, general and decisive issues of religion. It is the sect which follows the truth, the Quran and the Sunnah, and which follows the way of the Prophet, sallallaahu ‘alayhi wa sallam, and the Companions in terms of belief, manners and practice. It is, in brief, the Ahlus-Sunnah wal-Jamaa‘ah (the mainstream people of the Sunnah).
The Prophet, sallallaahu ‘alayhi wa sallam, clarified that this sect is the only one that will be saved from Hell. He said so in a Hadeeth indicating that the Muslims will split into 73 sects, all of whom will be in Hell except one, and that one is that which follows the way of the Prophet, sallallaahu ‘alayhi wa sallam, and his Companions . [Al-Haakim and others]
It is based on this standard that any other group can be measured: either Tableegh or others. Anything that agrees with the way of the Prophet, sallallaahu ‘alayhi wa sallam, his Companions and the righteous predecessors is the truth, regardless of the group or its membership. Please, also read Fataawa 88076 and 87749.
Allaah Knows best.