"And God blessed the seventh day" (Genesis 2:3). "The blessing of the LORD, it makes rich" (Proverbs 10:22), this is the Sabbath day; "and He adds no sorrow with it," this refers to mourning, as in the verse you say, "the king grieved over his son" (II Samuel 19:3).
The Blessing of the LORD Enriches and Adds No Sorrow
Yalkut Shimoni on Torah 16:18
וַיְבָרֶךְ אֱלֹהִים אֶת יוֹם הַשְּׁבִיעִי, (משלי י, כב) "בִּרְכַּת ה' הִיא תַעֲשִׁיר" זֶה יוֹם הַשַּׁבָּת "וְלֹא יוֹסִיף עֶצֶב עִמָּהּ", זֶה הָאָבֵל כְּמָה דְּאַתְּ אָמְרֵת (שמואל ב יט, ג) "נֶעֱצַב הַמֶּלֶךְ עַל בְּנוֹ".