Sahih Muslim
Sahih Muslim 1487, 1488 b
The Obligation to mourn during the 'Iddah following the death of one's husband, but it is forbidden to mourn for more than three days in other cases
Arabic hadith text
وَحَدَّثَتْهُ زَيْنَبُ، عَنْ أُمِّهَا، وَعَنْ زَيْنَبَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَوْ عَنِ امْرَأَةٍ مِنْ بَعْضِ أَزْوَاجِ النَّبِيِّ صلى الله عليه وسلم
Translation
This hadith was narrated by Zainab from her mother and from Zainab, the wife of Allah's Apostle (ﷺ), or from some other lady from among the wives of the Prophet (ﷺ).