Acts 13:33

That our children have had this promise completely fulfilled to them by God, by his raising Jesus. That is just what is said in the second Psalm--'Thou art my Son; this day I have become thy Father.'

Hebrews 5:5

In the same way, even the Christ did not take the honour of the High Priesthood upon himself, but he was appointed by him who said to him-- 'Thou art my Son; this day I have become thy Father';

Hebrews 1:5-6

For to which of the angels did God ever say-- 'Thou art my Son; this day I have become thy Father'? or again-- 'I will be to him a Father, and he shall be to me a Son'?

Treasury of Scripture Knowledge

Summary

God hath fulfilled the same unto us their children, in that he hath raised up Jesus again; as it is also written in the second psalm, Thou art my Son, this day have I begotten thee.

Bible References

Thou art

Hebrews 1:5
For to which of the angels did God ever say-- 'Thou art my Son; this day I have become thy Father'? or again-- 'I will be to him a Father, and he shall be to me a Son'?
Hebrews 5:5
In the same way, even the Christ did not take the honour of the High Priesthood upon himself, but he was appointed by him who said to him-- 'Thou art my Son; this day I have become thy Father';