Scriptural basis
The directive within the Quran (Al-Baqarah 2:228), regarding the waiting period for a divorcee, is:
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]
In surah Al-Ahzab it is stated:
O ye who believe! When ye marry believing women then divorce them before touching them then there is no iddah, you have reckon with. (Al-Quran 33:49)[8]
In the Quran surah At-Talaq Verse 65:4, it is stated:
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 directive within the Quran Surat At-Talaq 65:4, regarding the waiting period for "those who have no courses" (i.e. they are still young), is:
And those of your women as have passed the age of monthly courses, for them the ‘Iddah (prescribed period), if you have doubts (about their periods), is three months, and for those who have no courses (i.e. they are still immature) their ‘Iddah (prescribed period) is three months likewise, except in case of death.[10]
The Mohsin Khan translation also clarifies that this refers to those who have not yet menstruated, as they are "still immature".[11]
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 and also for those who have not yet menstruated because of their young age their period shall also be three months — both cases apply to other than those whose spouses have died; for these latter their period is prescribed in the verse they shall wait by themselves for four months and ten days.[12]
Tafsir ibn Kathir, says 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.[13]
The Tafsir al Jalalyn co-authored by the scholar Imam Suyuti says of 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[14]