All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Perhaps you refer to the hadeeth narrated by Anas ibn Maalik in which the Prophet, sallallaahu ‘alayhi wa sallam, said, "Have dinner, even if it is just a handful of bad dates, for missing dinner hastens old age." It was cited by At-Tirmithi, who classified it as Munkar (rejected). Also, Shaykh Al-Albaani, classified it as Dha'eef (weak) in his commentary on the ahaadeeth of Sunan At-Tirmithi.
Having dinner is a flexible matter; whoever wishes to have dinner may do so, and whoever wishes to skip it may do so. However, the one who has dinner should not sleep immediately after dinner in order to avoid indigestion. This is why physicians in the past and present advised walking after dinner. Ibn Al-Qayyim cited the statement of Al-Haarith ibn Kaladah, the renowned Arab physician, reading, "When one eats lunch, let him lay down for a while, and when he eats dinner, let him walk forty steps." [Zaad Al-Ma'aad]
Allah knows best.