Hadith 504270
Chapter 9: Shortening the Prayer - كتاب قصر الصلاة فى السفر
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَطَاءَ بْنَ يَسَارٍ، كَانَ إِذَا مَرَّ عَلَيْهِ بَعْضُ مَنْ يَبِيعُ فِي الْمَسْجِدِ دَعَاهُ فَسَأَلَهُ مَا مَعَكَ وَمَا تُرِيدُ فَإِنْ أَخْبَرَهُ أَنَّهُ يُرِيدُ أَنْ يَبِيعَهُ قَالَ عَلَيْكَ بِسُوقِ الدُّنْيَا وَإِنَّمَا هَذَا سُوقُ الآخِرَةِ .
Yahya related to me from Malik that he had heard that if some one passed by Ata ibn Yasar in the mosque with something to trade, he would call him and ask, "What is the matter with you? What do you want?" If the man said that he wished to trade with him, he would say, "You need the market of this world. This is the market of the next world."
Reference Muwatta Malik 504270
USC-MSA web (English) reference : Book 9, Hadith 95