ABSTRACT
Jewish and Christian influences on the fasts practiced in Islam have been treated by Orientalists on many occasions. Just as in the case of Judaism, Islam fully admits the expiatory virtue of fasting. After the fixing of the Jewish calendar in the fourth century, direct observation of the moon and the calculations based on such observations were abolished. There is lack of agreement between Judaism and Islam over different kinds of fasting, as appears frequently in the hadith. Ancient Islam was in fact familiar with a fast whose Jewish origin is clear even though the Muslim sources never connect it with Judaism: that is the fast of Mondays and Thursdays. Abu Hurayra ascribes this practice to the Prophet, who gives the same motive: "I like my acts to be presented at the time that I am fasting". The Monday-Thursday-Monday series of fasts is also familiar to Judaism.
