Urwah bin al-Zubayr (may Allah have mercy on him) said: The Messenger of Allah (peace and blessings be upon him) set out for Uhud. When he reached Uhud, Abdullah bin Ubayy went back from there with three hundred of his companions, and seven hundred remained with him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17862