Quran has made it clear in ample words that it was Ismael (sws) who was offered for sacrifice:
وَقَالَ إِنِّي ذَاهِبٌ إِلَى رَبِّي سَيَهْدِينِ. رَبِّ هَبْ لِي مِنَ الصَّالِحِينَ. فَبَشَّرْنَاهُ بِغُلَامٍ حَلِيمٍ.
فَلَمَّا بَلَغَ مَعَهُ السَّعْيَ قَالَ يَا بُنَيَّ إِنِّي أَرَى فِي الْمَنَامِ أَنِّي أَذْبَحُكَ فَانظُرْ مَاذَا تَرَى قَالَ يَا أَبَتِ افْعَلْ مَا تُؤْمَرُ سَتَجِدُنِي إِن شَاء اللَّهُ مِنَ الصَّابِرِينَ. فَلَمَّا أَسْلَمَا وَتَلَّهُ لِلْجَبِينِ. وَنَادَيْنَاهُ أَنْ يَا إِبْرَاهِيمُ. قَدْ صَدَّقْتَ الرُّؤْيَا إِنَّا كَذَلِكَ نَجْزِي الْمُحْسِنِينَ. إِنَّ هَذَا لَهُوَ الْبَلَاء الْمُبِينُ. وَفَدَيْنَاهُ بِذِبْحٍ عَظِيمٍ. وَتَرَكْنَا عَلَيْهِ فِي الْآخِرِينَ. سَلَامٌ عَلَى إِبْرَاهِيمَ. كَذَلِكَ نَجْزِي الْمُحْسِنِينَ. إِنَّهُ مِنْ عِبَادِنَا الْمُؤْمِنِينَ. وَبَشَّرْنَاهُ بِإِسْحَقَ نَبِيًّا مِّنَ الصَّالِحِينَ. وَبَارَكْنَا عَلَيْهِ وَعَلَى إِسْحَقَ وَمِن ذُرِّيَّتِهِمَا مُحْسِنٌ وَظَالِمٌ لِّنَفْسِهِ مُبِينٌ.
Abraham said: “[Leaving you aside, now] I will go towards my Lord. He will definitely guide me. Lord! Grant me righteous children. [As soon as Abraham prayed, in response] We gave him glad tidings of a forbearing boy. [That boy reached maturity.] Then when he reached the age to work about with him, Abraham said to him [one day]: “My son! [Since the past few days,] I dream that I am slaughtering you. So reflect; what is your opinion?” He said: “Father! Do as you are being directed. God willing, you will find me steadfast.” Then when both of them submitted and the father laid down his son on his forehead and We called out to him: “Abraham! You have made your dream come true,” imagine how the sea of mercy must have stirred. In reality, this is how We reward those who are thorough in their deeds. Surely, this was a clear trial. [When Abraham successfully came out of it,] We ransomed Ishmael against a grand sacrifice and [gave Abraham such fame that] We left a group among the earlier generations on his ways. Peace be to Abraham. Thus do We reward those who are thorough in their deeds. Undoubtedly, he was among Our believing servants. [It was at this instance that] We gave him glad tidings of Isaac; a prophet from among righteous. And We sent Our blessings to both Ishmael and Isaac. Now there are those in their progeny who are thorough in their deeds and also those who are openly unjust to their souls. (Quran 37:99-113)
(Excerpt from Al-Bayan: Javed Ahmed Ghamidi)
(Translated by Dr. Shehzad Saleem)
The Glad Tidings of Isaac( sws) (i.e. Verse 112) came after the incident of sacrifice which related to previous child whose glad tidings are mentioned in Verse 101.