Just believe?
Upon realizing that he has finally reached his goal, he was ecstatic. He was still doubting it though, since he knew Xue would basically kill him off, revive him, only to kill him again, if he is to tell this to her without any concrete proof. However, there came another problem. He didn't know what would constitute as a genuine proof that he actually reached the ancient realm. No one in his sect hadn't touched this realm in a really long time now that they didn't even have the records of the previous person who did it.
Well, the one who reached the ancient realm previously… He was truly a man of mystery for the people in his sect. He did challenge the God, but the only thing that people know of him was that he was beaten by the God once he fought him. Nothing else. He never returned back to his sect, or didn't leave any relevant information that would help the future generation. For reasons like this, people in Goldy's sect branded him as an extremely selfish person.