Answered by Shaykh Faraz Rabbani
If a person didn’t know to make niyya for their fasts, do they need to make it up?
The intention for fasting is very simple: it is to know in your heart that you will fast that day. It is valid to have this intention any time from maghrib the night before up to the Islamic midday of the actual day of fasting. [The Islamic midday is half way between the beginning of fajr and maghrib time.]
See Related Q&A on the fiqh of intention.
Q) what if they have a habit of rinsing their mouth on completion of the wudu, and forgetting to be careful, they accidentally swallow some water? is their fast still valid?
There are three ways something can enter your body cavity while fasting:
1. Deliberately. This breaks the fast;
2. Forgetfully. This does not, because of the Prophetic (Allah bless him & give him peace) guidance that it does not. (Otherwise, legal reasoning (qiyas) alone would have indicated that it does.)
3. Mistakenly/Accidentally. This breaks the fast. An example: what you mentioned; or if one ate thinking that fajr time had not come in or maghrib time come in, when the contrary was true.
Q) is it permissible to insert wetted fingers into the ear holes while making wudu while fasting?
Yes.
Walaikum assalam,