(O Prophet! Allah is Sufficient for thee and those who follow thee of the believers) [8:64].
Abu Bakr ibn al-Harith informed us> Abu'l-Shaykh al-Hafiz> Ahmad ibn 'Amr ibn 'Abd al-Khaliq> Safwan ibn al-Mughlis> Ishaq ibn Bishr> Khalaf ibn Khalifah>> Anas ibn Hashim al-Rummani> Sa'id ibn Jubayr> Ibn 'Abbas who said: “First, there were thirty-nine people who had embraced Islam and then 'Umar embraced Islam and they became forty. Gabriel, peace be upon him, brought down the words of Allah, exalted is He: (O Prophet! Allah is Sufficient for thee and those who follow thee of the believers)”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou