The Sabbath Epistle is a 12th-century polemical letter defending the traditional view that Shabbat begins at dusk, attributed to the biblical commentator Rabbi Abraham Ibn Ezra. In a preface, Ibn Ezra describes how he received a letter from Shabbat in a dream, instructing him to defend Shabbat. When he woke up, he discovered a commentary, presumably that of the Rashbam to Genesis 1:5, suggesting that a day in the Jewish calendar starts at dawn rather than the accepted view that a day begins at dusk. Realizing that this would lead to desecration of Shabbat, the Ibn Ezra set out to justify the traditional view. The work thus provides a general explanation of the Jewish calendar, incorporating astronomy and biblical interpretation.