What is meant by "And he calls Allah to witness as to what is in his heart"?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. He tells people: "Allah bears witness that what my tongue is saying is what is in my heart."
2. He says: "O Allah, bear witness to this statement of mine."