If a fasting person eats or drinks on purpose and knowingly, his fast is void
Fast Invalidators
Eating and Drinking
The Criterion of Eating and Drinking
If a fasting person eats or drinks on purpose and knowingly, his fast is void. It makes no difference whether it is among normal food and drink, or non-edible like a piece of cloth/paper, whether it is a lot or a little like a very tiny drop of water or a small crumb of bread.
Source: Hadana adopted from the Istiftaat of the Grand Ayatollah Khamenei
