Is it permissible to fast the Day of Arafah without a prior intention?

Fasting on the Day of Arafah is recommended and expiates the sins of two years. It does not require a prior intention; rather, it is sufficient to have the intention to fast from the night, or even from the day before eating and drinking. The fast is valid even if the intention is made after zawāl (zenith) according to the majority of scholars. Scholars differed on whether one receives the reward for the entire day or only from the time of the intention. The Hanbalis believe that one is rewarded from the time of the intention, whereas the Shafi'is believe that one receives the reward for fasting the entire day because the reward for fasting is not divisible, and this view has strength.