What is the basis for the obligation of the waiting period (Iddah)?

Primary text

The obligation of the waiting period is established by the Book (Quran), the Sunnah (Prophetic Tradition), and the Consensus (Ijma). Evidence from the Quran includes the verses: "Divorced women shall keep themselves waiting for three periods" (Quran 2:228), "And those who no longer expect menstruation among your women,- if you doubt, then their prescribed period of waiting shall be three months, and for those who have not menstruated as well. And for those who are pregnant, their term is that they lay down their burden" (Quran 65:4), and "Those of you who die and leave behind wives, they shall keep themselves waiting four months and ten days" (Quran 2:234). The evidence from the Sunnah includes the Prophet's saying, "It is not permissible for a woman who believes in Allah and the Last Day to mourn for a dead person for more than three (days), except for a husband, for whom she must wait four months and ten days." Furthermore, the Ummah has reached a consensus on the obligation of the waiting period in principle.