إِسْحَاقُ
Ishaq AS was a prophet, the son of Ibrahim AS, given as glad tidings to his wife Sarah, and the father of Ya'qub AS. Allah reserved prophethood among Ibrahim's descendants, and every prophet after Ibrahim came from Ishaq's line except the last, the Prophet ﷺ, who descended from Ismail AS. When the Quraysh tested the Prophet ﷺ about the family of Ya'qub, Allah revealed Surah Yusuf.
فَبَشَّرْنَاهَا بِإِسْحَاقَ وَمِن وَرَاءِ إِسْحَاقَ يَعْقُوبَ
“We gave her [Sarah] good tidings of Ishaq, and after Ishaq, Ya'qub.”
This ayah directly names Ishaq (AS) as the glad tidings given to Sarah, Ibrahim (AS)'s wife.
وَوَهَبْنَا لَهُۥٓ إِسْحَـٰقَ وَيَعْقُوبَ وَجَعَلْنَا فِى ذُرِّيَّتِهِ ٱلنُّبُوَّةَ وَٱلْكِتَـٰبَ
“We blessed him with Ishaq and [later] Ya'qub, and reserved prophethood and revelation for his descendants.”
This ayah directly names Ishaq (AS) among the line of prophethood Allah reserved for Ibrahim (AS)'s descendants.