I sat on a chair that might have touched an impure liquid. The cushion was washed, but I am unsure if the chair remains ṭāhir or if it needs purification. Would wiping it with a damp cloth be adequate, given its porous nature?
Bismihi ta'āla
The fact that you've said "might have touched" and "unsure" makes the scenario hold no weight. In matters of taharah and najasah, it is only certainty that you act upon. As long as the cushion was washed, that is more than enough, and dismiss your other thoughts.
And Allah knows best.