How do I control my tongue? What did the scholars say about speech?

"And the Qur'an is the speech of Allah; from Him it began, without modality, as a saying, and He sent it down upon His Messenger as revelation, and the believers testified to that as true, and they were certain that it is the speech of Allah Most High in very truth, not created as the speech of created beings is created. So whoever hears it and claims that it is the speech of a human being has disbelieved. And Allah has censured him and reproached him and threatened him with Saqar, where He said, Most High: Him shall I fling unto the burning. So when Allah threatened with Saqar the one who said: This is naught else than speech of mortal man, we knew and were certain that it is the speech of the Creator of mankind, and it does not resemble the speech of mankind."

"The second is guarding the tongue from idle chatter, lying, backbiting, gossiping, foul language, harshness, arguments, and disputes, instead obliging oneself to silence and occupying it with the remembrance of Allah and recitation of the Quran. This is the fasting of the tongue. Sufyan said that backbiting ruins the fast. Moreover, it is narrated that Mujahid said: "Two traits ruin fasting: backbiting and lying.""

"It is narrated that the Prophet, peace be upon him, said: "Five things break the fast of a fasting person: lying, backbiting, gossiping, false oaths, and lustful gazes." The second is guarding the tongue from idle chatter, lying, backbiting, gossiping, foul language, harshness, arguments, and disputes, instead obliging oneself to silence and occupying it with the remembrance of Allah and recitation of the Quran."

"How do you know? Perhaps he used to speak about what did not concern him and be stingy with what did not enrich him. Guard your tongue against eight things. First, lying. Guard it from lying in seriousness and jest. Do not accustom your tongue to lying in jest, lest it leads to lying in seriousness. Lying is among the greatest sins."

"so that their issuing from him is like the issuing of a lie from the tongue. Thus he profits neither from his tongue nor from his deeds. For this reason lying is the foundation of wickedness, as the Prophet said: "Lying leads to wickedness, and wickedness leads to the Fire." The first thing lying does is travel from the soul to the tongue and corrupt it; then it travels to the limbs A Section on the Words of God Most High"

"Rather, they only experience life to feel pain. The point is that when a person is in distress or calamity, their heart, tongue, and limbs fail them in what would be of most benefit to them. Their heart does not incline towards reliance on Allah, returning to Him, focusing on Him, supplicating, and humbling themselves before Him. Their tongue does not comply with remembrance, and even if they mention Allah by tongue, they do not unite their heart with their tongue, so that the remembrance becomes effective. Nor do their heart and tongue focus on the One Remembered. Instead, if they remember or supplicate, they"

"about what he feared from the people of Pharaoh concerning the slain man and the impediment of his speech, for there was an impediment on his tongue that prevented him from much speech. He asked his Lord to support him with his brother Aaron, to be an aid for him, to speak on his behalf concerning much that his tongue could not articulate. God Almighty granted him his request, loosened a knot from his tongue, and God revealed to Aaron and commanded him to meet with him. Moses set out with his staff until he met Aaron, and together they proceeded to Pharaoh. They stood at his gate for a while before finally"

"The other opinion is that it is not necessary to inform the person of the backbiting, slander, or insult. It is sufficient for the repentance to be between the individual and اللّٰه, and to mention the person wronged in positive terms in the places where they were previously slandered, replacing the backbiting with praise and commendation, and mentioning their virtues, and the slander with acknowledgment of their chastity and integrity, and to seek forgiveness for them to the extent of the backbiting."

"If enjoining good is avoided due to blame, slander, or criticism, then the obligation would be neglected entirely, as these risks are inherent. An exception is when the wrongdoing is slander, and one knows their objection would only lead to further slander. In this case, the duty is forbidden, as it increases the sin. However, if only the original slander remains, it is not compulsory to intervene, though it is commendable to shield the subject of the slander out of altruism."

"Then comes the defect of singing poetry, followed by the defect of joking; then mockery and derision; then revealing secrets; then false promises; then lying in speech and oaths; then the explanation of equivocation in lying; then backbiting; then carrying tales; then being duplicitous. Next is the flaw of flattery; next the neglect of subtle errors in the tenor of speech, particularly concerning Allah and His attributes."