ENOfficial
`Abdallah b. al-Harith b. Jaz' said he had seen no one more given to smiling than God's messenger. Tirmidhi transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَبْدِاللَّهِ بْنِ الْحَارِثِ بْنِ جَزْءٍ قَالَ: مَا رَأَيْتُ أَحَدًا أَكْثَرَ تَبَسُّمًا مِنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَوَاهُ التِّرْمِذِيّ
sunnah.com