Ahmad Ibn Aasim Al-Antaakee (rahimahullaah) lived in the generation of Bishr Ibn Al-Haarith (rahimahullaah); Ali Ibn Abdir-Rahmaan (rahimahullaah) said that Ahmad Ibn Aasim Al-Antaakee (rahimahullaah) said: The most beneficial intellect is (the one) that makes you acknowledge the blessings of Allaah and assists you in being thankful (i.e. by using those blessings to obey Allaah) and to be in opposition to (forbidden) desires.
He (rahimahullaah) was asked about sincerity, so he said: (It is) the performance of righteous deeds, whilst not wishing to be mentioned and exalted due to your deed, and not seeking a reward through your deed from anyone (besides Allaah). This is sincerity.
He (rahimahullaah) also said: If you are seeking rectification for your heart, then seek aid through that by restraining your tongue (i.e. restrain your tongue from evil speech, falsehood, the affairs that do not concern you etc).
[Source: Seerah As-Salaf As-Saaliheen of Imaam Ismaa’eel Ibn Muhammad Al-Asbahaanee (rahimahullaah); section: Those who followed the Taabi-een in goodness. Maktabah Shaamila]