In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Ibraaheem Bin Ad’ham [rahimahullaah] said: Abstinence from the worldly life is of three types: Obligatory abstinence; the abstinence that is of a superior virtue and the abstinence that is safety. As for the obligatory abstinence, it is abstinence from the unlawful; the abstinence that is of superior virtue is to abstain from what is lawful [but unnecessary]; and the abstinence that is safety is to abstain from the doubtful matters. [Jaami-ul Uloom Wal-Hikam: page:310]
Imaam Ibnul Qayyim [rahimahullaah] said: Whoever wants to attain the love of Allaah, then let him be dedicated to His remembrance [i.e. the remembrance of Allaah]. [Al-Waabilus Sayyib: page: 65]
He [rahimahullaah] said: Whoever shows you the perfection of the afterlife, then indeed he has made parting with this world insignificant. [Badaa’i Al-Fawaa’id: 2/222]
He [rahimahullaah] said: Whoever loves something will mention it a lot with his heart and tongue. And for this reason Allaah commanded His slaves to remember Him in all circumstances. [Uddatus Saabireen: 197]
He [rahimahullaah] said: Too much socialising, wishing for things, attachment to others besides Allaah, filling one’s stomach and sleep; these five affairs are amongst the greatest corrupters of the heart. [Uddatus Saabireen: 197]
Shaikh Abdur-Razzaaq Al-Badr [hafidhahullaah] said: Staying within the boundaries of Halaal and Haraam, and not coming close to the doubtful matters depends on the righteousness or corruption of a person’s heart. If the heart is pious and has that fear of falling into doubtful matters which can harm a person in the afterlife, it will distance itself from haraam and that which leads to Haraam. However, if the heart is corrupt, it will not care about falling into [error]. If the sickness in the heart is not too much, the heart engages in doubtful matters; and if the sickness increases, the heart engages in Haraam. If the corruption in the heart is not too much, the heart will not be safeguarded against the doubtful matters; and if the corruption is too much, the heart will not be safeguarded against what is forbidden. This shows the importance of rectifying one’s heart. [Source: Sharh Al-Arba’een, lecture number 9. Slightly Paraphrased]