(9) باب وُجُوبِ الإِحْدَادِ فِي عِدَّةِ الْوَفَاةِ وَتَحْرِيمِهِ فِي غَيْرِ ذَلِكَ إِلاَّ ثَلاَثَةَ أَيَّامٍ
'A'isha (Allah be pleased with her) reported Allah's Messenger (ﷺ) as saying:
It is not permissible for a woman believing in Allah and the Hereafter to observe mourning on the dead for more than three (days), except in case of her husband. (ID)
Reference (ID): Sahih Muslim 1491 (ID)
In-book reference (ID): Book 18, Hadith 84 (ID)
USC-MSA web (English) reference(deprecated numbering scheme): Book 9, Hadith 3549 (ID)