Ikrimah said: Ibn Abbas was informed that so-and-so, a certain wife of the Prophet (ﷺ), had died. He fell down prostrating himself. He was questioned: Why do you prostrate yourself this moment? He said: The Messenger of Allah (ﷺ) said: When you see a portent (an accident), prostrate yourselves. And which portent (accident) can be greater than the death of a wife of the Prophet (ﷺ).
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ عُثْمَانَ بْنِ أَبِي صَفْوَانَ الثَّقَفِيُّ، حَدَّثَنَا يَحْيَى بْنُ كَثِيرٍ، حَدَّثَنَا سَلْمُ بْنُ جَعْفَرٍ، عَنِ الْحَكَمِ بْنِ أَبَانَ، عَنْ عِكْرِمَةَ، قَالَ قِيلَ لاِبْنِ عَبَّاسٍ مَاتَتْ فُلاَنَةُ بَعْضُ أَزْوَاجِ النَّبِيِّ صلى الله عليه وسلم فَخَرَّ سَاجِدًا فَقِيلَ لَهُ أَتَسْجُدُ هَذِهِ السَّاعَةَ فَقَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا رَأَيْتُمْ آيَةً فَاسْجُدُوا " . وَأَىُّ آيَةٍ أَعْظَمُ مِنْ ذَهَابِ أَزْوَاجِ النَّبِيِّ صلى الله عليه وسلم
sunnah.com