Speaking falsehood is sinful. Does it mean speaking is the truth is no sinful? Sometimes by speaking truth, we fall into trouble. For example, my college is lazy in cleaning living room. When I tell, he is lazy, he becomes angry and speak no longer. So speaking truth can sometimes inflict on other. Please correct my opinion.
This page has extracts from a dozen suttas, which explain what "Right Speech" is.

Being "truthful" is an aspect, but  not the only aspect, of Right Speech: for example speech should also be affectionate and spoken with a mind of good-will, beneficial, and spoken at the right time. Also polite, not divisive, and so on.