that she got a Khul during the time of the Prophet. So the Prophet ordered her - or: she was ordered - that she observe an Iddah of a menstruation." (Using translation from Tirmidhī 1185)
اخْتَلَعَتْ عَلَى عَهْدِ النَّبِيِّ ﷺ فَأَمَرَهَا النَّبِيُّ ﷺ أَوْ أُمِرَتْ أَنْ تَعْتَدَّ بِحَيْضَةٍ