Siman 287
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א יְכוֹלִים לְנַחֵם אֲבֵלִים בְּשַׁבָּת, וְכֵן יְכוֹלִים לְבַקֵּר אֶת הַחוֹלֶה. וְלֹא יֹאמַר לוֹ כַּדֶּרֶךְ שֶׁאוֹמֵר לוֹ בַּחֹל, אֶלָּא אוֹמֵר לוֹ: שַׁבָּת הִיא מִלִּזְעֹק וּרְפוּאָה קְרוֹבָה לָבֹא, וְרַחֲמָיו מְרֻבִּים וְשִׁבְתּוֹ בְּשָׁלוֹם. הַגָּה: וְיֵשׁ אוֹמְרִים דְּאֵין צָרִיךְ לוֹמַר וְרַחֲמָיו מְרֻבִּים, וְכֵן נָהֲגוּ (רַמְבַּ"ם פֶּרֶק כ"ד).
1 Comforting Mourners and Visiting the Sick on Shabbos: We may comfort mourners on Shabbat and we may visit the sick. We do not speak to them the same way we speak to them during the week. Rather, we say to them “It is Shabbos, when it is forbidden to cry out; healing will [surely] come soon, for His mercies are abundant; rest on Shabbos in tranquility". Rema: There are those who say that we do not have to say 'His mercies are abundant' and such is the custom. (Rambam)