Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.107.

Section : Fasting (As-siyam).

As-Siyam generally means “to abstain from something.” For example, a verse in the Qur’an says: “I have vowed to the Merciful to abstain – that is, from speaking.

What is meant here is abstaining from food, drink, and sexual intercourse from dawn until sunset with the explicit intention of doing so (for the sake of Allah).