As-Suyootee said in Badhiyyatul-Wi’aat (1/62): "His books have no equal and he strove and traversed the path of the great Imaams in tafseer, hadeeth, fundamentals (usool), the branches (furoo’) and the ‘Arabic language."

His student, the scholar of tafseer, al-Haafidh ibn Katheer, wrote about him in al-Bidaayah wan-Nihaayah (14/246):

"He attained great proficiency in many branches of knowledge, particularly knowledge of tafseer, hadeeth and usool. When Shaykh Taqiyyud-Deen ibn Taymiyyah returned from Egypt in the year 712H, he stayed with the Shaykh until he died, learning a great deal of knowledge from him, along with the knowledge he had already occupied himself in obtaining. So he became a singular scholar in many branches of knowledge. He also continued to seek knowledge greatly day and night and was constant in humbly calling upon his Lord. He recited well and had fine manners. He had a great deal of love and did not harbour any envy for anyone, nor harm anyone, nor seek to find fault with anyone, nor bear any malice towards anyone. I was one of those who most often kept company with him and I was one of the most beloved of people to him. I do not know of anyone in this world in this time who is a greater worshipper than him. His Salaah used to be very lengthy, with prolonged bowing and prostration. His companions would often reproach him for this, yet he never retorted back, nor did he abandon this practice - may Allaah shower His Mercy upon him."

Another of his students, al-Haafidh ibn Rajab, said in Dhayl Tabaqaatul-Hanaabilah (4/450):

"He rahimahullah was constant in worship and performing the tahajjud Prayer, reaching the limits in lengthening his Salaah and devotion. He was constantly in a state of Dhikr and had an intense love for Allaah. He also had a deep love for turning to Allaah in repentance, humbling himself to Him with a deep sense of humility and helplessness. He would throw himself at the doors of Divine obedience and servitude. Indeed, I have not seen the likes of him with regards to such matters."

Mullah ‘Alee al-Qaaree said in al-Mirqaat (8/251) that both ibn Taymiyyah and ibn al-Qayyim were:

"... from the great ones of Ahlus-Sunnah wal-Jamaa’ah and from the awliyaa of this Ummah."