Narrated Abu Dhar (RA):

Allah's Messenger (ﷺ) said to me, "Say the truth even though it is bitter (i.e. difficult to admit)." [Ibn Hibban graded it Sahih (authentic) as a part of a long Hadith].

عَنْ أَبِي ذَرٍّ ‏- رضى الله عنه ‏- قَالَ: قَالَ لِي رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ قُلِ اَلْحَقَّ, وَلَوْ كَانَ مُرًّا } صَحَّحَهُ اِبْنُ حِبَّانَ فِي حَدِيثٍ طَوِيلٍ [1]‏ .‏