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
وَحَدَّثَنَاهُ شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي ابْنَ مُسْلِمٍ - حَدَّثَنَا عَبْدُ، اللَّهِ بْنُ دِينَارٍ عَنْ نَافِعٍ، بِإِسْنَادِ حَدِيثِ اللَّيْثِ . مِثْلَ رِوَايَتِهِ .
A hadith like this is transmitted on the authority of Nafi'.