Parashat Chayei Sara tells the story of Yitzchak’s marriage to Rivka, the daughter of his first cousin. Avraham assigned his servant the task of finding a suitable mate for Yitzchak, and upon the servant’s return with Rivka, they encountered Yitzchak, who had gone out into the field “la-su’ach” (24:63). The Gemara in Masekhet Berakhot (26b; see also Bereishit Rabba 60:14) interprets this term as a reference to prayer, and thus infers from this verse that Yitzchak instituted the afternoon mincha service. A verse in Tehillim (102:1), as the Gemara cites, s