Sayyiduna Wa'il bin Hujr (may Allah be pleased with him) said: I came to the Prophet (peace and blessings be upon him), and my hair was (long), so he (peace and blessings be upon him) said: "Dhubab!" (meaning, it is bad). I went and had some of my hair cut, then came to him (peace and blessings be upon him), and he (peace and blessings be upon him) said to me: "Why did you have your hair cut?" I said: I heard you (peace and blessings be upon him) saying "Dhubab", so I thought you were finding fault with me. He (peace and blessings be upon him) said: "I did not find fault with you, and this is better."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18319