I never saw anyone who smiled more often than the Messenger of Allah ﷺ.
ما رأيت أحدا أكثر تبسما من رسول الله ﷺ.
Tirmidhi related it in his Sunan (3641) and in Shamail (228) from Qutayba bin Saeed, and Ibn Mubarak related it in Zuhd (145). Abu Shaykh related it in Akhlaq Nabi ﷺ (p. 63) through Abdullah bin Yazid Muqri. All three of them narrated from Ibn Lahia, from Ubaydullah bin Mughira, from Abdullah bin Harith bin Juz, who said, then he mentioned it.Its isnad is hasan. Ibn Lahia has been discussed by scholars regarding his memory, but this hadith was narrated from him by Abdullah bin Mubarak, Abdullah bin Yazid Muqri, and Qutayba bin Saeed, and their narrations from him are sound and accepted by the meticulous scholars.It has also been narrated from Jabir bin Samura, who said, "There was slenderness in the shins of the Messenger of Allah ﷺ, and he would never laugh except with a smile. Whenever I looked at him, I would say, 'His eyes appear lined with kohl, though they are not actually lined with kohl.'" However, this is daif.Tirmidhi related it in his Sunan (3645) and in Shamail (226), and Ahmad (21004), and Hakim graded it sahih (2/606). All of them narrated it through Abbad bin Awwam, who said, "Hajjaj bin Artah informed us, from Simak bin Harb, from Jabir bin Samura," who said, then he mentioned it.Its isnad is daif because of Hajjaj bin Artah, for he is a mudallis, in addition to the criticism regarding his memory. Hakim said, "The isnad is sahih." But Dhahabi rejected this and said, "It contains Hajjaj, and he is weak in hadith."