Sahih al-Bukhari 1858
Narrated As-Sa'ib bin Yazid:
(While in the company of my parents) I was made to perform Hajj with Allah's Messenger (ﷺ) and I was a 
seven-year-old boy then. (Fath-ul-Bari, p.443, Vol.4)
حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ يُونُسَ، حَدَّثَنَا حَاتِمُ بْنُ إِسْمَاعِيلَ، عَنْ مُحَمَّدِ بْنِ يُوسُفَ، عَنِ السَّائِبِ بْنِ يَزِيدَ، قَالَ حُجَّ بِي مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَنَا ابْنُ سَبْعِ سِنِينَ‏.‏