Pirkei DeRabbi Eliezer continues and says that Yitzchak mourned for Sarah his mother for three years. After three years, he took Rivka and the mourning ended. Seemingly, why did he mourn for three years when it is known that mourning does not extend beyond a year?
The sefer Velo Od Ela writes that it is difficult to understand why he mourned beyond the period set by Chazal, since the Avot observed the entire Torah. Furthermore, why specifically three years, no less and no more? However, it appears, as previously mentioned, that she cried three cries corresponding to three shofar blasts (tekiyot), three wails corresponding to three sobs (yevavot), and her soul departed and she died. It is true that Sarah Imeinu died from the sorrow she heard from the Satan that her son was not slaughtered, and she was distressed, saying, "Was he not accepted as a burnt offering before Hakadosh Baruch Hu?" and from this sorrow, she died. But the world did not know or understand this and took the matter literally, saying she died from the sorrow that her son was subjected to this distress, which is a disgrace to Sarah, as it seems she was not confident in Avraham's faith. Therefore, due to this desecration that arose, Yitzchak accepted mourning for three years; not actual mourning, but he conducted himself with seriousness and refrained from joys to atone for the three cries and three wails in which she died, and this brought about slander in the world.
