Fulfillment of promises is one of the noble traits with which the intelligent people adorn themselves:
“Mention in the Book (the Quran) the story of Ishmael; he was true to his promise, a Messengers and a Prophet. (19:54)"
As he promised a man, Ishmael the prophet confined himself in one place for a whole year waiting for him so as to keep his promise.
It is unfortunate that breach of promise, nowadays, has become a common phenomenon among Muslims who neglected its disadvantages that weaken the mutual confidence, corrupt the social relations, and harm the public interests.
Imam as-Sadiq (a) said: “The promise of the believer is a ransomless vow. He who reneges breaks his word with Allah and exposes himself to His dislike. This is the meaning of Allah’s saying: Believers, why do you preach what you do not practice? It is most hateful in the sight of Allah if you say something and do not practice it. (61:2-3)"
The Prophet (s) once, promised he would wait for a man near a rock. When the heat of the sun became
so intense, the Prophet’s companions suggested to him to stand in the shadow until that man would come. “No," said he, “I promised him to wait near this r ock. If he does not come, that will be his fault." )
source : http://www.maaref-foundation.com