Sunan Ibn Majah 132
سنن ابن ماجه#132SahihIt was narrated that Hashim bin Hashim said:"I heard Sa'eed bin Musayyab say: 'Sa'd bin Abu Waqqas said: 'No one else became Muslim on the same day as I did; for seven days I was one-third of Islam
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiSahih