Sahih Bukhari Volume 8, Book 82, Hadith 6598

حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا يَزِيدُ الرِّشْكُ، قَالَ سَمِعْتُ مُطَرِّفَ بْنَ عَبْدِ اللَّهِ بْنِ الشِّخِّيرِ، يُحَدِّثُ عَنْ عِمْرَانَ بْنِ حُصَيْنٍ، قَالَ قَالَ رَجُلٌ يَا رَسُولَ اللَّهِ أَيُعْرَفُ أَهْلُ الْجَنَّةِ مِنْ أَهْلِ النَّارِ قَالَ ‏"‏ نَعَمْ ‏"‏‏.‏ قَالَ فَلِمَ يَعْمَلُ الْعَامِلُونَ قَالَ ‏"‏كُلٌّ يَعْمَلُ لِمَا خُلِقَ لَهُ ـ أَوْ لِمَا يُسِّرَ لَهُ‏"‏ ‏.‏

Narrated By Imran bin Husain : A man said, "O Allah's Apostle! Can the people of Paradise be known (differentiated) from the people of the Fire; The Prophet replied, "Yes." The man said, "Why do people (try to) do (good) deeds?" The Prophet said, "Everyone will do the deeds for which he has been created to do or he will do those deeds which will be made easy for him to do." (i.e. everybody will find easy to do such deeds as will lead him to his destined place for which he has been created).