Sunan an-Nasa'i, Hadith 3526 ⓘ
It was narrated from 'Aishah that the Prophet said: "It is not permissible for a woman who believes in Allah and the Last Day to mourn for more than three days, except for her husband."
أَخْبَرَنَا مُحَمَّدُ بْنُ مَعْمَرٍ، قَالَ حَدَّثَنَا حَبَّانُ، قَالَ حَدَّثَنَا سُلَيْمَانُ بْنُ كَثِيرٍ، قَالَ حَدَّثَنَا الزُّهْرِيُّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ أَنْ تَحِدَّ فَوْقَ ثَلاَثَةِ أَيَّامٍ إِلاَّ عَلَى زَوْجٍ " .
also referenced under: Book 27, Hadith 138 (In-Book) & Volume 4, Book 27, Hadith 3556 (DarusSalam)