(15) بَابُ مَنَاقِبُ سَعْدِ بْنِ أَبِي وَقَّاصٍ الزُّهْرِيِّ وَبَنُو زُهْرَةَ أَخْوَالُ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَهْوَ سَعْدُ بْنُ مَالِكٍ
Narrated Sa`d bin Abi Waqqas:
No man embraced Islam before the day on which I embraced Islam, and no doubt, I remained for seven days as one third of the then extant Muslims.
Reference: Sahih al-Bukhari 3727
In-book reference: Book 62, Hadith 75
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 57, Hadith 73