The Messenger of Allah ﷺ said, "I do joke, but I only speak the truth."
قال رسول الله ﷺ: إني لأمزح، ولا أقول إلا حقا.
No references are available.
Tabarani narrated it in Al-Awsat (999) and in Al-Saghir (779) through various routes from Hushaym bin Jamil, who said, Mubarak bin Fadala told us, from Bakr bin Abdullah Muzani, from Ibn Umar, who said, and then he related it.Its chain of transmission is hasan because of Mubarak bin Fadala, for there is some criticism of him that does not harm his standing, since his hadith has a firm basis. Haythami also graded it hasan in Al-Majma (8/89).