The Messenger of Allah ﷺ said, "What an excellent people the Azd are, sweet in speech, true to their oaths, pure in heart."
وبإسناده قال رسول الله ﷺ نعم القوم الأزد طيبة أفواههم برة أيمانهم نقية قلوبهم
Its isnad is hasan. "Barrah aymanuhum" means their oaths are truthful. It is said, "He was true (barra) in his oath," meaning he spoke the truth.