A man said to Salmaan al-Faarisee (radiyallaahu-anahu), ”Advise me!” He said: ”Do not speak.” He (the man) said, ”I am not able to live amongst the people without speaking.” He (Salmaan) said, ”If you speak, then speak the truth or keep silent.”

[Source: Jaami-ul Uloom Wal-Hikam: page:144]