In The Name of Allaah, The Most Merciful The Bestower of Mercy.
He [radiyallaahu-anhu] said: “Indeed, you see an unbeliever with the healthiest body amongst the people and with the sickest heart; and you will come across a believer with the most upright of hearts and the unhealthiest body [i.e. physical illness]. I swear by Allaah, if your hearts were sick and your bodies healthy, you will be more insignificant to Allaah than dung beetles”.
He [radiyallaahu-anhu] said: “’Search for your heart in three situations [i.e. how you respond]: When the recitation of the Qur’aan is heard, in the gatherings where Allaah is remembered and in times of seclusion. If you do not find your heart in these situations, then ask Allaah to grant you a heart, for indeed you do not have a heart’’.
He [radiyallaahu-anhu] said: “Sins take control over the heart”.
He [radiyallaahu-anhu] said: “Indeed, the people make their speech very good and appropriate; the one whose speech is in conformity with his actions is that one who has achieved his portion of [goodness]. And the one whose speech is in opposition to his actions, then he is that one who has rebuked himself’’.
He [radiyallaahu-anhu] said: “There is not anything on the face of the earth more needed than a prolonged imprisonment of the tongue [i.e. speak good or remain silent]’’.
[Source: Al-Fawaa-id by Imaam Ibnul Qayyim [rahimahullaah]. page 213-221]