Mazal tov ??

Hi Shavua tov. I have 2 questions. a) From where does the statement ’Mazal-tov" come from b) If we say that Am Yisrael does not have Mazal so why do we wish each other "mazal-tov"

The saying "Mazal Tov" is found in the "Kiddush Levana" prayer for the new moon. The earliest source for this prayer is found in "Masechet Sofrim" Chapter 19:1. (According to the Rosh and Chida in Birkei Yosef Masechet Sofrim is dated to the Geonic period. (הרא"ש בהל ס"ת בענין פרשה פתוחה (סי' יג), ברכי יוסף אורח חיים סימן תקפב ס"ק ז, ) Regarding your second question if the Talmud ( Shabbat 156) says that "There is no Mazal in regard to the Jewish People" then why do we wish "Mazal Tov"? In simple terms, the Talmud seems to be saying that we are not dependent upon what is in "store" in the "mazalot" and there is nothing which cannot be changed by bringing ourselves closer to Hashem and mending our ways. However, if to begin with Hashem had good things in store for us then we would like to be bestowed and blessed so that indeed we indeed receive that good. So Mazal Tov (See Ibn Ezra Shmot 6:13, Rashba Responsa 1:19, 5:48, Rabbi Moshe Chaim Luzatto=Ramchal - Derech Hashem, 2:7:3-4)