Risalaatus Haqiqatus Siyaam was a small Risalaah written by Ash-Shaykh Al-Islaam Ibn Taymiyyah explaining the obligations and the invalidators of fasting. The commentary of the book is by Ash-Shaykh Al-Allaamah Muhammad Saalih Al-Uthaymeen (May Allaah have mercy upon both of them) printed on yellow paper. 414 pages