Hadithcore
Sahih al-Bukhari, 530
sahih

Narrated Az-Zuhri that he visited Anas bin Malik at Damascus and found him weeping and asked him why he was weeping. He replied, "I do not know anything which I used to know during the life-time of Allah's Messenger (ﷺ) except this prayer which is being lost (not offered as it should be)."

حَدَّثَنَا عَمْرُو بْنُ زُرَارَةَ، قَالَ أَخْبَرَنَا عَبْدُ الْوَاحِدِ بْنُ وَاصِلٍ أَبُو عُبَيْدَةَ الْحَدَّادُ، عَنْ عُثْمَانَ بْنِ أَبِي رَوَّادٍ، أَخِي عَبْدِ الْعَزِيزِ قَالَ سَمِعْتُ الزُّهْرِيَّ، يَقُولُ دَخَلْتُ عَلَى أَنَسِ بْنِ مَالِكٍ بِدِمَشْقَ وَهُوَ يَبْكِي فَقُلْتُ مَا يُبْكِيكَ فَقَالَ لاَ أَعْرِفُ شَيْئًا مِمَّا أَدْرَكْتُ إِلاَّ هَذِهِ الصَّلاَةَ، وَهَذِهِ الصَّلاَةُ قَدْ ضُيِّعَتْ‏.‏ وَقَالَ بَكْرٌ حَدَّثَنَا مُحَمَّدُ بْنُ بَكْرٍ الْبُرْسَانِيُّ أَخْبَرَنَا عُثْمَانُ بْنُ أَبِي رَوَّادٍ نَحْوَهُ‏.‏

References2 variants
In-Book Reference
Book 9, Hadith 9
USC-MSA web (English) reference
Vol. 1, Book 10, Hadith 507 (deprecated numbering scheme)