The Book of Divorce
18/9. Chapter:
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
Sahih Muslim
وَحَدَّثَنَاهُ أَبُو غَسَّانَ الْمِسْمَعِيُّ، وَمُحَمَّدُ بْنُ الْمُثَنَّى، قَالاَ حَدَّثَنَا عَبْدُ الْوَهَّابِ، قَالَ سَمِعْتُ يَحْيَى بْنَ سَعِيدٍ، يَقُولُ سَمِعْتُ نَافِعًا، يُحَدِّثُ عَنْ صَفِيَّةَ بِنْتِ أَبِي عُبَيْدٍ، أَنَّهَا سَمِعَتْ حَفْصَةَ بِنْتَ عُمَرَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم تُحَدِّثُ عَنِ النَّبِيِّ صلى الله عليه وسلم بِمِثْلِ حَدِيثِ اللَّيْثِ وَابْنِ دِينَارٍ وَزَادَ " فَإِنَّهَا تُحِدُّ عَلَيْهِ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا " .
Safiyya bint Abu 'Ubaid reported that she heard Hafsa daughter of Umar (Allah be pleased with them), (and) wife of Allah's Prophet (ﷺ), narrating a hadith like this from Allah's Apostle (ﷺ), and she made this addition: " She should abstain from adorning herself (in case of the death of her husband) for four months and ten days."
Reference : Sahih Muslim 1490cIn-book reference : Book 18, Hadith 82USC-MSA web (English) reference : Book 9, Hadith 3547