دَخَلْتُ عَلَى أَنَسِ بْنِ مَالِكٍ بِدِمَشْقَ وَهُوَ يَبْكِي فَقُلْتُ مَا يُبْكِيكَ فَقَالَ لاَ أَعْرِفُ شَيْئًا مِمَّا أَدْرَكْتُ إِلاَّ هَذِهِ الصَّلاَةَ، وَهَذِهِ الصَّلاَةُ قَدْ ضُيِّعَتْ.
Az-Zuhri reported: I entered upon Anas ibn Malik in Damascus while he was weeping. I asked, “What makes you weep?” He said, “I do not recognize anything of what I witnessed except this prayer, and this prayer has (also) been neglected.”
also in Sahih al-Bukhari 529