Answer
Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
If a person has doubt whether he nullified his ablution or not, then his original state of being pure remains and his doubt does not have any effect.
Answering your question, the late Saudi scholar, Sheikh Ibn Baz (may Allah have mercy on him) stated:
If a person has doubt whether he nullified his ablution or not, then his original state of being pure remains and his doubt does not have any effect. This is based on the Prophet’s statement, when a man asked him about feelings he has in his stomach during the prayer,
“Do not leave [the prayer] until you hear a sound or you perceive a smell.” (Al-Bukhari and Muslim)
The Prophet (peace be upon him) made it clear to him that the basic ruling is that of purity until one is certain that something has occurred to nullify it.
As long as the person is simply in doubt, his state of purity is sound and confirmed. Therefore, he may continue to pray, circumambulate the Ka`bah, read the Qur’an from a mushaf and so forth. That is the original ruling. This is, all praises are due to Allah, from the magnanimity and easiness of Islam.
Almighty Allah knows best.
Source: Islamic Fatawa Regarding Women, Compiled by Muhammad Ibn Abdul-Aziz Al-Musnad and translated by Jamal Al-Din Zarabozo, Darussalam, 1996.