Killing your child because god says so
Ibrahim who had not seen his son since he was a baby, came back to Makkah to visit him. Upon arriving, he heard that Hajar had died, but Ismail was still living there. Ibrahim was yearning to see his son whom he loved and missed a lot. He saw Ismail under a tree near Zamzam, sharpening his arrows. When he saw his father, Ismail rose up, hugged him and greeted him. It was the happiest moment for both father and son. But Allah wanted to put them to test, and it was a tough test indeed. During one night, Ibrahim had a dream. He came to Ismail and said: "O my son ! I have seen in a dream that I am slaughtering you as a sacrifice to Allah, so what do you think?" They both realized that this was an order from Allah. Ismail said without hesitation: "Do what you are commanded, you shall find me very patient insha Allah." They had both submitted to the will of Allah. Ibrahim laid his son prostrate, put his forehead on the ground and directed a sharp knife towards his neck. At this very moment, Allah called him: "O Ibrahim! You have fulfilled the dream! Thus do We reward the good doers !" A big sheep was sent down from heaven to be slaughtered instead of Ismail, which Ibrahim did, and they both had a big celebration that day. This event is celebrated every year by all Muslims. It is Eid al-Adha where we slaughter the sacrificial sheep.
Ibrahim and Ismail kept on calling people to worship Allah. At that time there was no place built for the worship of Allah. Ibrahim wished there could be such a place where people would be in peace, and concentrate solely for the worship of Allah. His wish was answered when Allah ordered him to build the Sacred House, the Ka'bah. Ibrahim said to Ismail: "O Ismail, Allah has given me an order, will you help me execute it?" "Yes I will." Ismail said. "Allah has ordered me to build a house here." He said, pointing to a hillock higher than the land surrounding it. They went towards the place and started building the foundations of the Ka'bah Ismail brought the stones and Ibrahim built the walls, and when the walls became high, Ismail brought a large stone and put it in front of his father who stood over it and carried on building, while Ismail was handing him the stones. Both of them went on building and going around the Ka'bah, saying: "O our Lord accept this service from us." When they finished the building, Angel Jibreel descended from heaven and showed Ibrahim the rituals of Hajj. Then Ibrahim stepped on the stone and called on people: "O people obey your Lord." This large stone which Ibrahim stepped on is still there to this day near the Ka'bah. It is called Makam Ibrahim.
Thus ends the story of Ibrahim, the father of the prophets. From him descended all the prophets who came later, including Muhammad, sallallahu alayhe wa sallam. Ibrahim devoted all his life calling others to the True religion: Islam. Alone he stood against his people, his father, and even the mighty king of Babylon, and never flinched. Yet his method was always to gradually persuade them by bringing irrefutable proofs, that most often embarrassed those who refused to accept the Truth, but as Allah said: "Any whom Allah leaves to stray, there is none to guide !"