Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "When the son of Adam gets up in the morning, all of his body organs humble themselves before the tongue, and say: 'Fear Allah concerning us! For indeed, we are only as you are (our condition depends upon yours); if you are upright, we shall be upright, and if you are crooked, we shall be crooked.’"
Meaning of the Hadīth: All body organs submit and humble themselves before the tongue, i.e. they are subordinate to the tongue. That is why when one gets up in the morning, they say: “Fear Allah concerning us! For indeed, we are only as you are…” The tongue is the most dangerous organ. If it is upright, all other organs will be upright and the rest of one's deeds will be good. However, if the tongue is crooked, all of the organs will be crooked and the rest of one's deeds will be evil. Anas (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "A slave’s faith will not be upright unless his heart is upright, and his heart will not be upright unless his tongue is upright." This chapter includes many Hadīths that indicate the danger of the tongue. It is either a source of happiness or a reason for punishment. If one subjugates it to the obedience of Allah, then it will be a source of happiness for him in this world and the Hereafter. However, if he lets it loose in that which does not please Allah, the Exalted, it will be a reason for regret in this world and the Hereafter.