Reason for Difference about Waiting Period and Waiting Period of a Widow

“I once asked abu Ja‘far, al-Thaniy (a.s.), saying, ‘I pray to Allah to keep my soul in service for your cause, why is it that waiting period for a woman divorced three times, is three cycles of Hayd (menses) or three months, and the waiting period of a widow is four months and ten days? He (the Imam) said, ‘Waiting period for a woman divorced three times is passing of three Hayd (menses)- free periods. It is to ascertain a womb is free of child and pregnancy. About the waiting period of a widow Allah, most Majestic, most Glorious, has set a condition for and a condition against women. In the condition for them He does not hold them accountable and in the condition against them He has not done injustice to them. In the case of ’Ila’ (swearing not to go to bed with one’s wife) it is four months as Allah, most Majestic, most Glorious, says, ‘. . . for those who swear there is a four month waiting period.’ (2:226) He has not made it permissible for anyone in the case of ‘Ila’ to wait more than four months because He, most Blessed, most High, knows how long women can wait without going to bed and without men. The condition against women is in the case of the death of their husband in which case they must wait for four months and ten days. Thus He has taken from her when he dies as much as He has takes for her from him during his life time in the case of ‘Ila’ as Allah, most Blessed, most High, says, ‘. . . they must wait for four months and ten days.’ He has not mentioned the ten days in waiting period except with four months. He knows that women can wait without men only for four months and without going to bed. For this reason He has set conditions for and against them.’”