Muhammad bin Ishaq said: Sayyiduna Amr bin al-As (may Allah be pleased with him), Sayyiduna Khalid bin al-Walid and Sayyiduna Uthman bin Talhah (may Allah be pleased with him) accepted Islam in the presence of the Negus, and then they came to Madinah in the month of Safar in the eighth year of the Hijrah. (Allamah al-Haythami says:) I say: That these men accepted Islam on one and the same day is well known; but as for Sayyiduna Khalid (may Allah be pleased with him) and Sayyiduna Uthman bin Talhah (may Allah be pleased with him) accepting Islam with the Negus,
I have found this only as a statement of Ibn Ishaq. And Allah knows best.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب المناقب / 15892