What are the matters to which Islam has guided us for the preservation of our tongues and the purification of our souls?

The revealed texts urge the guarding of the tongue and warn against its danger, based on the Almighty's saying: "He utters no word except that with him is an observer, ready [to record]", and the Prophet's (peace be upon him) saying: "Whoever believes in Allah and the Last Day, let him speak good or remain silent." The Prophet (peace be upon him) was asked about what most causes people to enter Hellfire, and he said: "The mouth and the private parts." What purifies the soul and brings one closer to Allah is piety towards Allah, observing His obligations, staying away from His disobedience, frequently remembering Allah, reciting the Quran, accompanying the righteous, and attending gatherings of knowledge.