One Intention for the Whole Month?
Question:
Does every day on which the fast is performed in Ramadan require an intention, or is it sufficient to make one intention for the whole month?
Answer:
It is sufficient in Ramadan to make one intention at the beginning of it, because even if the fasting person did not make an intention for every day the night before, that was has intention at the start of the month. But if the fasting is broken during the month due to a journey, or illness or the like, he must make the fresh intention, because he has broken it by abandoning the fast due to travel, illness or the like.
Shaykh Muhammad bin Saalih al-`Uthaymeen
Islamic Verdicts on The Pillars of Islaam, vol.2, page.644
http://www.fatwaislam.com/fis/index.cfm?scn=fd&ID=692