Ibraheem (AS) was childless until the age of 86; That is when Allah bestowed him with a righteous son, Ismael (AS) through Hajar (AS). His wife Sarah was infertile and could not have children. Ibraheem (AS) lived with Sarah (AS), while Isamael (AS) and Hajar (AS) lived in Makkah.
One day, some strangers came to his house. He brought a meal to serve them, but they did not eat.
“And verily, there came Our Messengers to Ibraheem (Abraham) with glad tidings.They said: Salâm (greetings or peace!) He answered, Salâm and he hastened to entertain them with a roasted calf.” (69)
“But when he saw their hands went not towards it (the meal)[i.e. they did not eat], he felt some mistrust of them, and conceived a fear of them. They said: “Fear not, we have been sent against the people of Lout ” (70)
Ibraheem’s (AS) guests were in fact angels sent to punish the people of Lout (AS) and to give the glad tidings of Ishaq (AS) to Ibraheem (AS) and Sarah (AS).
“And his wife was standing[Sarah] (there to serve/entertain them), and she laughed ( for being glad for the destruction of the people of Lout (AS)(Lot) because of their evil ways). But We gave her glad tidings of Ishâq(Isaac), and after him, of Ya’qûb (Jacob).” (71)
Sarah (AS) on hearing this was very surprised as she knew she was old and infertile as well.
“She said (in astonishment): “Woe unto me! Shall I bear a child while I am an old woman, and here is my husband, an old man? Verily! This is a strange thing!” (72)
“They (angels) said: “Do you wonder at the Decree of Allâh? The Mercy of Allâh and His Blessings be on you, O the family [of Ibraheem ]. Surely, He (Allâh) is All-Praiseworthy, All-Glorious.” (73)
At another point in Quran, it is mentioned:
“They (the angels) said: “Do not be afraid! We give you glad tidings of a boy (son) possessing much knowledge and wisdom (Ishaq)” (53)
“[Ibrâheem ] said: “Do you give me glad tidings (of a son) when old age has overtaken me? Of what then is your news?” (54)
“They (the angels) said: “We give you glad tidings in truth. So be not of the despairing ones.”(55)