Maybe there is an argument in Shabbis 156 lwhether there is a mazel for Jews. We pasken that we are above the mazel as we can change it through tefila or maasim tovim, so we wish one that it should stay as it is good and not be changed.
Rava in Moad Katan 28,1 says that children. the length of life and sustinance is dependent on the mazel but it can be changed as above and deducted from one’s zechusim.
It seems like I am not the only one who can’t find the mekor. lol
Also wondering how old this minhag is? Do we find such words in Chazal for wellwishing? I know we say it by Kiddush Levanah but couldn’t find source for that either…..
So wish them “long life and happiness” or”do you know what you are getting into” or “hopefully it will work out for both of you”. Whatever seems most appropriate for the couple, time and place.
I don’t know if this is an actual mekor, but we find in the Chumash that when Leah Imeinu gave the name Gad, Rashi there says “Ba Mazel Tov” (Beraishis 30:11)