Where should the woman whose husband died observe her waiting period?

It was narrated from Zainab bint Ka'b bin 'Ujrah, who was married to Abu Sa'eed Al-Khudri,:
that his sister Furai'ah bint Malik said: "My husband went out to pursue some slaves of his. He caught up with them at the edge of Qadumttl and they killed him. News of his death reached me when I was in one of the houses of the Ansar, far away from the house of my family and my brothers. I went to the Prophet ﷺ and said: 'O Messenger of Allah ﷺ, there has come to me news of my husband's death and I am in a house far away from the house of my people and the house of my brothers. He did not leave any money that could be spent on me, or any inheritance, or any house I may take possession of. If you think that you could give me permission to join my family and my brothers, then that is what I prefer and is better for me in some ways.' He said: 'Do that if you wish.' Then I went out, feeling happy with the ruling of Allah given upon the lips of the Messenger of Allah ﷺ, until, when I was in the mosque, or, in one of the apartments, he called me and said: 'What did you say?' I told him the story, and he said: 'Stay in the house in which the news of your husband's death came to you, until your waiting period is ever."' She said: "So I observed the waiting period there for four months and ten (days)."

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، سُلَيْمَانُ بْنُ حَيَّانَ عَنْ سَعْدِ بْنِ إِسْحَاقَ بْنِ كَعْبِ بْنِ عُجْرَةَ، عَنْ زَيْنَبَ بِنْتِ كَعْبِ بْنِ عُجْرَةَ، وَكَانَتْ، تَحْتَ أَبِي سَعِيدٍ الْخُدْرِيِّ أَنَّ أُخْتَهُ الْفُرَيْعَةَ بِنْتَ مَالِكٍ، قَالَتْ خَرَجَ زَوْجِي فِي طَلَبِ أَعْلاَجٍ لَهُ فَأَدْرَكَهُمْ بِطَرَفِ الْقَدُومِ فَقَتَلُوهُ فَجَاءَ نَعْىُ زَوْجِي وَأَنَا فِي دَارٍ مِنْ دُورِ الأَنْصَارِ شَاسِعَةٍ عَنْ دَارِ أَهْلِي فَأَتَيْتُ النَّبِيَّ ﷺ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّهُ جَاءَ نَعْىُ زَوْجِي وَأَنَا فِي دَارٍ شَاسِعَةٍ عَنْ دَارِ أَهْلِي وَدَارِ إِخْوَتِي وَلَمْ يَدَعْ مَالاً يُنْفِقُ عَلَىَّ وَلاَ مَالاً وَرِثْتُهُ . وَلاَ دَارًا يَمْلِكُهَا فَإِنْ رَأَيْتَ أَنْ تَأْذَنَ لِي فَأَلْحَقَ بِدَارِ أَهْلِي وَدَارِ إِخْوَتِي فَإِنَّهُ أَحَبُّ إِلَىَّ وَأَجْمَعُ لِي فِي بَعْضِ أَمْرِي . قَالَ " فَافْعَلِي إِنْ شِئْتِ " . قَالَتْ فَخَرَجْتُ قَرِيرَةً عَيْنِي لِمَا قَضَى اللَّهُ لِي عَلَى لِسَانِ رَسُولِ اللَّهِ ﷺ حَتَّى إِذَا كُنْتُ فِي الْمَسْجِدِ - أَوْ فِي بَعْضِ الْحُجْرَةِ - دَعَانِي فَقَالَ " كَيْفَ زَعَمْتِ " . قَالَتْ فَقَصَصْتُ عَلَيْهِ فَقَالَ " امْكُثِي فِي بَيْتِكِ الَّذِي جَاءَ فِيهِ نَعْىُ زَوْجِكِ حَتَّى يَبْلُغَ الْكِتَابُ أَجَلَهُ " . قَالَتْ فَاعْتَدَدْتُ فِيهِ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا .