(Ambiya') 21 : 72
وَوَهَبْنَا لَهُ إِسْحَاقَ وَيَعْقُوبَ نَافِلَةً ۖ وَكُلًّا جَعَلْنَا صَالِحِينَ
And We gave him Ishaaq, and then Ya’qoob, and We made them all righteous.
While Ibrahim was informed about the herald of son Ishaaq, he was also informed about the grandson Ya’qoob (Israel). From this, it is clear that Ismael was the first child of Ibrahim who was ordered to be sacrificed. See explanation 1: 6; 4: 69-70 and 11: 71.