《北史·列传·卷三十五》
阳固因为过去曾任过元悦的郎中令，虽然已经离开，仍然上疏恳切劝谏。后来，元悦征请他任从事中郎，他没有接受。
固以前为元卿，虽离国，犹上疏切谏，事在《悦传》。后悦辟固为从事中郎，不就。
Because Yang Gu had served as Yuan Yue's Langzhong Order in the past, although he had left, he still wrote a petition to advise him earnestly. Later, Yuan Yue invited him to serve as a member of the staff, but he did not accept.