Colossians 3:8; Ephesians 4:29,31; James 3; James 1:26; Matt 12:33-34; Luke 6:44-45; Ephesians 5:4
This is also by the command that we will be judged by every idle word at Christ's coming(Matt 12:36-37) so we should abstain from all forms of speech that do not edify to Godliness.