This mantra is mentioned in Yajurveda chapter 3 mantra 60 and Rigveda mandal 7 sukt 59 mantra 12. The mantra is "TREYAMBAKAM YAJAMAHE SUGANDHIM PUSHTIVARDHNAM URVARUKMIV BANDHNANMRITYORMUKSHIY MAMRITAT" (Rigveda 7/59/12).

Sugandhim = having fame, pushtivardhnam = who increases powers, treyambakam = who save us in past, present and future, yajamahe = we worship that God, urvarukmiv = like ripened musk melon, bandhnat = from binding, mrityoh= from death, mukshiy = to be free, amritat= from salvation, ma, aa= not.

Full meaning:
We worship the God who is having fame, increases power and who saves us. May I be free from death like ripened musk melon and one should not be away from getting salvation. Here is a word yajamahe, which means to worship daily and to be attached with God. So we must worship daily while doing yajna and jaap of holy name of God. And by practicing ashtang yoga. This is what the mantra is telling. So according to mantra we must worship the God whose qualities have been described in the mantra. And this mantra must be chanted while doing Yajna (Yagya) offering our aahuti of ghee and samagri in havan kund. We have to follow the order of the mantra. Suppose we do not worship to do Yajna or to do jaap of holy name of God, then it is of no use of mere chanting. So one thing is clear that its name is not Mahamritanjay mantra. It is Rigveda and Yajurved’s mantra which tells us about God.