It is narrated from Sayyidah Umm Ayyash (may Allah be pleased with her); she said: Sayyidah Ruqayyah (may Allah be pleased with her) bore a son to Sayyiduna Uthman (may Allah be pleased with him), and the Messenger of Allah (peace and blessings be upon him) named him Abdullah and gave Sayyiduna Uthman (may Allah be pleased with him) the kunyah Abu Abdullah.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21697