Second: The material he received directly from his own teachers.
He explicitly names two shaykhs from whom he heard in person:
He says (p. 508): “Shaykh al-Islam narrated to me: ‘One of the quick-witted—who had studied under the foremost scholar of his age in kalām and philosophy, Ibn Wāṣil al-Ḥamawī—told me…’”
He also says in Chapter Twelve (p. 131): “For this chapter we shall be content to mention a debate that took place between a Jahmī negationist and a Sunni affirming theologian. The substance of it was related to me by our shaykh, ʿAbd Allāh Ibn Taymiyyah (may Allah have mercy on him).”

Third: What he transmits from the scholars.
Imām Ibn al-Qayyim was fond of books and amassed a vast and varied library. Ibn Kathīr states in al-Bidāyah wa-l-Nihāyah (18/524): “He acquired books to a degree that no one else could have secured even a tenth of—works of both the early and later scholars.” Al-Ṣafadī says in Aʿyān al-ʿAṣr (4/368): “No one gathered as many books as he did, for he spent his lifetime procuring them. When our shaykh Fath al-Dīn (1) died, he bought from his estate many cornerstone and major foundational works. He owned something on every subject, in every discipline and school, often keeping multiple copies of the same book.”

I have compiled the titles of the works from which Imām Ibn al-Qayyim quotes in the extant portion of this book, and they number one hundred and twenty-five, namely: