A חסיד was asked what is the source of the מנהג to drink לחיים? He answered as follows: “The תורה is the source for everything, including this. The תורה tells us that פרעה made a משתה on his birthday. But why doesn’t it state which birthday it was? The answer is because we can deduce on our own that it was his fortieth birthday. The גמרא says: עד ארבעין שנין מיכלא מעלי. מכאן ואילך משתה מעלי. Since פרעה was celebrating his fortieth birthday, when drink becomes more important than food, it was on that day that he hung the שר האופים and restored the שר המשקים to his position.”
05/07/2020