Let him speak good or keep silent

On the authority of Abu Hurayra (may Allah be pleased with him), that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever believes in Allah and the Last Day, let him speak well or remain silent. Whoever believes in Allah and the Last Day, let him honour his neighbour. Whoever believes in Allah and the Last Day, let him honour his guest."

Related by al-Bukhari and Muslim.

[al-Bukhari 6018; Muslim 47]