Arabic text
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: «لا ينبغي لصِدِّيق أن يكون لعَّانًا».
Translation
Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "It does not befit the truthful person to frequently curse others."
Explanation
Frequent cursing contradicts the perfection of truthfulness, which is a rank next to the rank of prophet-hood. It is one of the highest ranks that the believer may attain with Allah, the Exalted. Among the means to attain the rank of truthfulness is to avoid cursing.
Source: HadeethEnc.com