Allah said about Ismail (as), انه كان صادقالوعد meaning, He was truthful to His promise. Awf ibn Uthman (ra) said, it’s better for a person to die of thirst then to break a promise. This means that you said you would do something for someone and didn’t do it.
Imam Ahmad (rh) was asked, how do you know the liars? He said, by their appointments.