Ibn Mudrik al-Taḥḥān; ʿAbd Allah ibn ʿAbd al-Raḥmān al-Dārimī; Muḥammad ibn Muslim ibn Wārah; Yaʿqūb al-Fasawī; al-Kudaymī; ʿUbayd Allah ibn Ḥajjāj ibn Minhāl; his son, Ḥammād ibn Yaḥyā ibn Ḥammād; Abū Muslim al-Kajjī; and many others.

Abū Ḥātim and a number of other scholars declared him reliable.
Ibn Saʿd said, “He was trustworthy and narrated extensively.” (1)
Muḥammad ibn al-Nuʿmān ibn ʿAbd al-Salām remarked, “I have never seen anyone more devoted in worship than Yaḥyā ibn Ḥammād, and I do not think he ever laughed.” (2)

I say: A little laughter—and still better, a simple smile—is preferable. Senior scholars who refrain from both do so for one of two reasons.
The first is praiseworthy: a person leaves off laughter out of refined etiquette, fear of Allah, and sorrow for his own needy soul.
The second is blameworthy: someone avoids it out of foolishness, arrogance, or mere posturing.
Likewise, whoever laughs excessively is held in low esteem; and there is no doubt that laughter is lighter and more excusable in youth than in old age.

As for smiling and a cheerful face, they are superior to all of that. The Prophet ﷺ said, “Your smile in your brother’s face is an act of charity.” (3)

Jarīr said, “The Messenger of Allah ﷺ never saw me…"