بسم الله الرحمن الرحيم
The following question was presented to the world renowned scholar of fiqh Ash-Shaykh Muhammad ibn Salih Al Uthaymin may Allah be merciful to him.
Q: Does every (single) day that is fasted during Ramadan necessitate a (renewed) intent or is it sufficient to intend to fast the entire month?
A: One intention at the beginning of Ramadan is sufficient. That’s because the fasting person if he does not renew his intent each day (the night before) then surely that was his intent at the beginning of the month. However if there is a break in fasting during the month due to traveling or sickness and whatever is similar to that, then renewal of the intention is made binding upon him, due to the intent being broken by abandonment of the fast due to traveling or a sickness etc.
Translated by Najeeb ibn Yusuf Al Anjelesi
Source: فتاوى في أحكام الصيام