Some rabbinical sources indicate that even before the covenant of Abraham, the aposthia of Shem may have been an inspiration for circumcision, although the aposthia of Shem is not specifically mentioned in the text of Genesis. During the Babylonian exile, Sabbath and circumcision became the characteristic symbols of the Jewish people. However, the Talmud orders that a boy must not be circumcised if he had two brothers, from the same mother as him, who have died as a result of their circumcisions; this may be due to a concern about haemophilia.