All truth is safe, and nothing else is safe; and he who keeps back the truth, or withholds it from men, from motives of expediency, is either a coward or a criminal, or both.

Max Müller (1823-1900) German-British philologist, Orientalist, religious studies founder

(Attributed)
    (Source)

This is frequently cited to Muller's The Science of Religion (1872), a collection of lectures, but does not appear there. The earliest reference seems to be in the Introduction and advertisements of T. W. Doane, Bible Myths and their Parallels in Other Religions (1882). While most of the block of text Doane attributes to Muller can be found in Muller's Lecture 1, this phrase does not.