Sahih Al Bukhari 1: Chapter 4, Hadith 137

(137) One should not repeat ablution if in doubt unless and until he is convinced (that he has lost his ablution by having Hadath)

حَدَّثَنَا عَلِيٌّ بْنُ عَبْدِ اللهِ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا سُفْيَانُ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا الزُّهْرِيُّ، ‏‏‏‏‏‏عَنْ سَعِيدِ بْنِ الْمُسَيِّبِ. ح وَعَنْ عَبَّادِ بْنِ تَمِيمٍ، ‏‏‏‏‏‏عَنْ عَمِّهِ، ‏‏‏‏‏‏أَنَّهُ شَكَا إِلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الرَّجُلُ الَّذِي يُخَيَّلُ إِلَيْهِ أَنَّهُ يَجِدُ الشَّيْءَ فِي الصَّلَاةِ، ‏‏‏‏‏‏فَقَالَ:‏‏‏‏ "لَا يَنْفَتِلْ أَوْ لَا يَنْصَرِفْ حَتَّى يَسْمَعَ صَوْتًا أَوْ يَجِدَ رِيحًا".

SAHIH HADITH:

Narrated `Abbas bin Tamim: My uncle asked Allah's Apostle about a person who imagined to have passed wind during the prayer. Allah' Apostle replied: He should not leave his prayers unless he hears sound or smells something.

REFERENCE:

Sahih Al Bukhari 1: Chapter 4, Hadith 137