On another occasion the question was put to him, what hope is? and his answer was, “The dream of a waking man.”

[ἐρωτηθεὶς τί ἐστιν ἐλπίς, “ἐγρηγορότος,” εἶπεν, “ἐνύπνιον.”]

Aristotle (384-322 BC) Greek philosopher

Attributed in Diogenes Laërtius, Lives and Opinions of Eminent Philosophers [Vitae Philosophorum], Book 5, sec. 11 [tr. Yonge (1853)]
    (Source)

(Source (Greek)). Alternate translations:

He was asked to define hope, and he replied, "It is a waking dream."
[tr. Hicks (1925), sec. 18]

When asked what hope is, he said “It is dreaming while awake.”
[tr. @sentantiq (2016), 5.21]

When asked to define hope, he said, "It is a waking dream."
[tr. Mensch (2018)]