直言不諱

More likely from the Book of Odes, Vol. VI (《卜居》):

寧正言不諱，以危身乎？將從俗富貴，以媮生乎？ [Classical Chinese, trad.]

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宁正言不讳，以危身乎？将从俗富贵，以偷生乎？ [Classical Chinese, simp.]

From: The Verses of Chu, 4^th century BCE – 2^nd century CE

Nìng zhèngyán bùhuì, yǐ wēi shēn hū? Jiāng cóngsú fùguì, yǐ tōushēng hū? [Pinyin]

Whether I should speak my mind without reservation, thus risking my life, or join the stream, covetous of wealth and position, thus dragging out my ignoble existence?

Note that although the contemporary work Yanzi Chunqiu also has a similar phrase 出言不諱, it is still not as famous as the text quoted above, which was not only attributed to the great poet Qu Yuan but included in Guwen Guanzhi, too. Also, 正 (zhèng) and 直 (zhí) are parasynonymous.

直言不諱

1. to call a spade a spade; to speak without reservation; not to mince one's words