Daniel 7:1 (BSB)

In the first year of the reign of Belshazzar over Babylon, Daniel had a dream, and visions passed through his mind as he lay on his bed. He wrote down the dream, and this is the summary of his account.

From Daniel 7. Also in the ESV.

Commentary on Daniel 7:1

• John Calvin (Reformed), Calvin's Commentaries on Daniel 7:1: Hear. Daniel begins to offer instruction peculiar to the Church. For God had formerly appointed him an interpreter and instructor to, profane kings. But he now appoints him a teacher to the Church, that he may exercise his office within it, and instruct the sons of God in the bosom of the Church.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Daniel 7:1-8: The date of this chapter places it before ch. 5, which was in the last year of Belshazzar, and ch. 6, which was in the first of Darius; for Daniel had those visions in the first year of Belshazzar, when the captivity of the Jews in Babylon was drawing near a period.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Daniel 7:1: In the first year of Belshazzar king of Babylon,.... Daniel having finished the historical part of his book, and committed to writing what was necessary concerning himself and his three companions, and concerning Nebuchadnezzar, Belshazzar, and Darius the Mede, proceeds to the prophetic part, and goes back to the first year of Belshazzar's reign, seventeen years before his death, and the fall of the Babylonish...
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on Daniel 7:1: In the first year of Belshazzar king of Babylon Daniel had a dream and visions of his head upon his bed: then he wrote the dream, [and] told the sum of the matters. (a) Whereas the people of Israel looked for a continual peace, after the seventy years which Jeremiah had declared, he shows that this rest will not be a deliverance from all troubles, but a beginning.