From Sahih Bukhari (Hadith 2652):
Narrated `Abdullah:The Prophet (ﷺ) said, "The people of my generation are the best, then those who follow them, and then those who follow the latter. After that there will come some people whose witness will go ahead of their oaths, and their oaths will go ahead of their witness." Ibrahim (a sub-narrator) said, "We used to be beaten for taking oaths by saying, 'I bear witness by the Name of Allah or by the Covenant of Allah
Reference: Bukhari 2652