Ibn Al Qayyim said,
“I was always surprised by the strength of Ibn Taymiyyah. It amazed me how much strength and Iman he had.”
One day he asked Ibn Taymiyyah about his ability to do all of this, and the Shaykh Al Islam said that the supplication / adhkar he said everyday in the morning and the night are what gave him the strength to write, read, teach, and debate to the extent that one time one of his students said that Ibn Taymiyyah would sit making adhkar from after fajr until close to dhuhr time, and he asked him if he did this every day. Ibn Taymiyyah replied that without it, he could not function.