הלכה אויף תהילים 137:6

The blessing for the Promised Land must begin and end with thanksgiving and its concluding formula is "for the land and for the food". Whoever omits in this blessing the phrase, "a land, desirable, good and ample" has not fulfilled his duty. The Abrahamic covenant and the Torah must also be mentioned in it. The reference to the Covenant must come first, since the covenant referred to in the benediction for the land is the rite of circumcision in connection with which there were thirteen covenants, while in connection with the Torah there were only three, as it is said, "These are the words of the Covenant" (Deuteronomy 28:69); "beside the Covenant which He made with them in Horeb" (ibid. 28:69); "Ye stand this day … that thou shouldst enter into the Covenant (ibid. 29:9-11).

And they also ordained that one who sets a table to make a meal for guests lack a little from it and leave an empty place without one of the bowls that it is fit to place there; and that when a women makes [herself up with] silver and gold jewelry, she leaves off one of the types of jewelry to which she is accustomed, such that the jewelry not be complete; and that when a groom marries a woman, he takes burnt ashes and puts it on his head in the place of where the tefillin lay. And all of these things are so as to remember Jerusalem, as it is stated (Psalms 137:5-6), "If I forget you, O Jerusalem, let my right hand wither. Let my tongue stick to my palate if I cease to think of you, if I do not raise up Jerusalem above my highest joy."

Should any of these four fast days occur during the bridegroom's seven days of wedding feast, although these days (of the wedding feast) are considered to him as a Yom Tov, nevertheless, he must fast.¹This law also applies when any of these fast days is postponed, as stated in paragraph 6. A groom must fast even on a postponed fast day. (Mishnah Berurah 559:9,35) Since his Yom Tov is only a personal celebration, the public mourning and fasting overrides it, and also, because it is written, "… if I fail to elevate Jerusalem above my foremost joy" (Psalms 137:6).