Did something happen that you're actually certain about — like hearing a clear sound or feeling something definite — or is it more of a vague feeling or doubt? Both answers are below — read the one that matches your situation.
If you're certain something happened
You're certain something specific happened — you heard or felt a clear, definite sign.
What to know
When there's genuine certainty, your wudu is broken and needs to be renewed before you pray. The confirmed nullifiers include passing wind, urination, defecation, deep sleep, and loss of consciousness.
What you can do
Perform wudu again from the start before praying.
If this happened in the middle of salah, stop, renew your wudu, and restart the prayer from the beginning.
Worth knowing: A few other matters — like touching your spouse, or blood flowing from a wound — are genuine points of difference between the madhhabs. If one of those applies to you and you're unsure, it's worth checking your specific school of thought.
You have a vague feeling or doubt, but nothing you're actually certain happened.
What to know
There's a specific, well-established principle here: certainty is not overturned by doubt. Your wudu stays valid until you're genuinely sure it's broken — a feeling, a suspicion, or background anxiety isn't enough on its own.
What you can do
Continue exactly as you were — praying, or going about your day — without renewing your wudu.
The Prophet ﷺ specifically addressed this: don't leave the prayer or assume your wudu broke unless you hear a sound or notice a smell that confirms it.
If the doubt keeps returning, it's often waswasah (repetitive intrusive doubt) rather than a real signal — the guidance is to firmly ignore it, not to keep checking.