Answer
The pillar of fasting is to abstain from satisfying the desires of the belly and the private parts; because Allah, the Exalted, permitted eating, drinking, and intimacy during the nights of Ramadan; as He said: {It is lawful for you to approach your wives on the night of fasting} until His saying {So now approach them and seek that which Allah has decreed for you. And eat and drink until the white thread of dawn becomes distinct to you from the black thread.} That is: until the light of day becomes clear from the darkness of night at dawn. Then He commanded to refrain from these things during the day with His saying: {Then complete the fast until the night.} This indicates that the pillar of fasting is as we said, and fasting does not exist without it. As mentioned in Tabyin al-Haqaiq 1: 313.