Hadith Q25
إِذِ الطَّهَارَةُ بِيَقِينٍ لَا تَزُولُ بِشَكٍّ وَارْتِيَابٍ، وَإِنَّمَا يَزُولُ الْيَقِينُ بِالْيَقِينِ، فَإِذَا كَانَتِ الطَّهَارَةُ قَدْ تَقَدَّمَتْ بِيَقِينٍ لَمْ تُبْطَلِ الطَّهَارَةُ إِلَّا بِيَقِينِ حَدَثٍ
Because certain purity is not nullified by doubt or suspicion; certainty is only nullified by certainty. Therefore, the previously existing certain purity will only be invalidated by certain impurity.
Hadith 25
Sayyiduna Abdullah bin Zaid (may Allah be pleased with him) narrates that I asked the Messenger of Allah (peace and blessings be upon him) about a person who feels something during prayer. He (peace be upon him) said: "He should not leave (the prayer) unless he hears a sound or perceives a smell."