Ibraaheem Ibn Adham (rahimahullaah) wrote to Sufyaan Ath-Thawri (rahimahullaah), saying:
”Whoever knows what he is seeking for (i.e. paradise etc), he will belittle what he carries out of deeds. Whoever allows his eye sight to roam freely (i.e. looking at everything), his sorrow will be prolonged. Whoever prolongs his hopes (i.e. in coveting the worldly pleasures etc), he will commit evil deeds. And whoever allows his tongue to speak freely (i.e. uttering evil or that which does not concern him etc)  has killed himself.”
[Source: ‘Seerah As-Salaf As-Saaliheen’ of Al-Asbahaanee (rahimahullaah)
Chapter: A mention of the Atbaa at-Taabi’een 1/970. (Maktabah Shaamilah)