ENOfficial
It was narrated that Zainab bint Umm Salamah said: "Umm Habibah said: 'I heard the Messenger of Allah (ﷺ) say: It is not permissible for a woman who believes in Allah and the Last Day to mourn for anyone who dies for more than three days, except for a husband; (she mourns for him for) four months and ten (days)."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا هَنَّادُ بْنُ السَّرِيِّ، عَنْ وَكِيعٍ، عَنْ شُعْبَةَ، قَالَ حَدَّثَنِي حُمَيْدُ بْنُ نَافِعٍ، عَنْ زَيْنَبَ بِنْتِ أُمِّ سَلَمَةَ، قَالَتْ أُمُّ حَبِيبَةَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ تَحِدُّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثَةِ أَيَّامٍ إِلاَّ عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا " .
sunnah.com