In Islam, a woman must observe the period of waiting, known as ’iddah or iddat (Arabic: العدة, romanized: al-ʿidda; "period of waiting") following the death of her husband or a divorce, during which she is prohibited from getting married to another man.^{[1]: 472 [2]} Eliminating any uncertainty regarding the paternity of a child born after the previous husband's divorce or death is one of its primary goals.

The duration of 'iddah varies depending on several factors. A divorced woman's 'iddah is typically three lunar months, or roughly 89 days; however, if the marriage was not consummated, there is no 'iddah. Whether or not the marriage was consummated, a woman's 'iddah is four lunar months and ten days (about 128 days) following her husband's passing. The 'iddah continues until the woman gives birth if she is pregnant at the time of her divorce or widowhood.

According to Islamic scholars, this directive strikes a compromise between allowing the widow to grieve her husband's passing and shielding her from potential criticism if she remarries too soon after.^[3] As four and a half months is half the duration of a typical pregnancy, this is often used to determine if a woman is pregnant or not.^[4]

The Quran (Al-Baqarah 2:234–235) gives the following instructions about a widow's waiting period:

If any of you die and leave wives behind, they shall wait concerning themselves four months and ten days: When they have fulfilled their term, there is no blame on you if they dispose of themselves in a just and reasonable manner. And God is well acquainted with what ye do. There is no blame on you if ye make an offer of betrothal or hold it in your hearts. God knows that ye cherish them in your hearts: But do not make a secret contract with them except in terms Honourable, nor resolve on the tie of marriage till the term prescribed is fulfilled. And know that God Knoweth what is in your hearts, and take heed of Him; and know that God is Oft-forgiving, Most Forbearing. Al-Baqarah 2:234-235 Translation Yusuf Ali (Orig. 1938)^[5]

The primary instructions (for widows) found in these passages are summarised as follows:

1. A widow's waiting period (Iddah) is four months and ten days;
2. The woman is not allowed to wed another man during this time;
3. A person may announce his plans to marry the widow during this time in a way that is socially acceptable or he may keep them to himself, but he should not make a covert marriage vow to the widow; and
4. Only after the four months and ten days have passed should the time and location of the marriage contract be decided upon and committed to.

These are the fundamental Sharia guidelines for a widow's waiting time. Another Quranic command makes it very evident that the woman should not be forced to leave her home during this waiting period.^[6]

The Quran (Al-Baqarah 2:228) gives the following instructions about a divorcee's waiting period:

Divorced women shall wait concerning themselves for three monthly periods. Nor is it lawful for them to hide what God Hath created in their wombs, if they have faith in God and the Last Day. And their husbands have the better right to take them back in that period, if they wish for reconciliation. And women shall have rights similar to the rights against them, according to what is equitable; but men have a degree (of advantage) over them. And God is Exalted in Power, Wise. Al-Baqarah 2:228 Translation Yusuf Ali (Orig. 1938)^[7]

The surah Al-Ahzab states:

O you who have believed, when you marry believing women and then divorce them before you have touched them [i.e., consummated the marriage], then there is not for you any waiting period to count concerning them. So provide for them and give them a gracious release. — (Al-Quran 33:49)^[8]

The surah At-Talaq Verse 65:4, in the Quran states:

Such of your women as have passed the age of monthly courses, for them the Iddah, if ye have any doubts, is three months, and for those who have no courses (it is the same): for those who carry (life within their wombs), their period is until they deliver their burdens: and for those who fear Allah, He will make their path easy. At-Talaq 65:4 Translation Yusuf Ali (Orig. 1938)^[9]

The primary instructions (for divorces) found in these verses are summarised as follows:

1. A lady who is menstruation must wait three months between cycles.
2. The waiting period for a pre-menstrual girl is, three lunar months
3. For a lady without monthly courses, the waiting period is three months.
4. If the husband wishes to make amends, he has a greater right to take her back during this time. But only in the event of a first or second divorce is this true.
5. There is no ’iddah if a Muslim man marries a Muslim lady and then divorces her before any physical relationship.

According to Imam Suyuti's commentary, Tafsir al-Jalalayn, "And as for those of your women who read allā’ī or allā‘i in both instances no longer expect to menstruate, if you have any doubts about their waiting period, their prescribed waiting period shall be three months. Additionally, for those who have not yet menstruated due to their young age, their period shall also be three months." These situations apply to everyone except those whose spouses have passed away, in which the verse specifies that they must wait four months and ten days on their own.^[10]

Tafsir ibn Kathir, comments thus of this verse,

Her Iddah is three months instead of the three monthly cycles for those who menstruate, which is based upon the Ayah in (Surat) Al-Baqarah. (see 2:228) The same for the young, who have not reached the years of menstruation. Their `Iddah is three months like those in menopause.^[11]

The Tafsir al Jalalyn co-authored by the scholar, Imam Suyuti comments thus about this verse

And [as for] those of your women who (read allā’ī or allā’i in both instances) no longer expect to menstruate, if you have any doubts, about their waiting period, their prescribed [waiting] period shall be three months, and [also for] those who have not yet menstruated, because of their young age, their period shall [also] be three months^[12]

And those who carry (life within their wombs), their iddah is until they deliver their burdens (Al-Quran 65:4)

Pregnant widows and pregnant divorced women are not allowed to be married again until after giving birth. Until there is no longer any uncertainty over any current pregnancy, remarriage is not permitted.^[13]