This is taken from Saviours Of Islamic Spirit by Shaykh Abul Hasan Ali Nadwi.
One of his bitterest rivals, Allama Kamal ud-din al-Zamalkani, has paid a glowing tribute to Ibn Taimiyah's encyclopaedic knowledge in these words :
"God had made knowledge of all the sciences as easy for Ibn Taimiyah as iron had been softened for (the prophet) David. Whenever he was asked any question, he answered in a way that the audience thought him to have spent his whole life in acquiring knowledge of that very branch of knowledge alone and acknowledged him as the greatest authority on the subject. Scholars subscribing to different juristic schools attended his discourses and each one of them learnt something that he had not known earlier. It never happened that he debated any point and was put to shame. Whatever be the subject matter about which he spoke, whether religious or discursive, he surpassed all the authorities on that particular subject. In penmanship, too, he was equally elegant." (Al-Kawakib-ud-Durriyah, p. 5)