Sunan Ibn Majah, Volume 3, Book 10, Hadith 2085 (DarusSalam) ⓘ
It was narrated from 'Aishah that: the Prophet said: "It is not permissible for a woman to mourn for any deceased person for more than three days, except for her husband."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ " لاَ يَحِلُّ لاِمْرَأَةٍ أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثٍ إِلاَّ عَلَى زَوْجٍ " .
also referenced under: Hadith 2085 (Reference) & Book 10, Hadith 2163 (In-Book)