I say, and with God's success: The most likely is that he is his eldest son, Ishmael. This is the view of Abdullah ibn Umar, Sa'id ibn al-Musayyib, al-Suddi, al-Hasan al-Basri, Mujahid, al-Rabi' ibn Anas, Muhammad ibn Ka'b al-Qurazi, al-Kalbi, and Abu 'Amr ibn al-Ala. It is also a narration from Ibn Abbas as reported by al-Baghawi from them. The scholars have elaborated on the evidence for this, which can be referred to in the interpretation of Ibn Kathir. And God knows best.