One of the Companions said:
You are doing deeds that are, in your eyes, more insignificant than a hair, whereas at the time of the Messenger of Allaah (‘alayhis-salaam) we would consider them to be destructive sins! 
ibn Rajab, the Journey to Allah
 al-Bukhaaree no. 6492 on the authority of Anas.
1747. Narrated ‘Abdullaah bin Mas’ood (radhi Allaahu anhu) : Allaah’s Messenger (Sallallaahu Alaihi Wasallam) said,
Allaah is more pleased with the repentance of His slave than a man who encamps at a place where his life is in jeopardy, but he has his riding animal carrying his food and water. He then rests his head and sleeps for a short while and wakes to find his riding animal gone. (He starts looking for it) and suffers exhausion from severe heat and thirst or what Allaah wished (him to suffer from). He then says, ‘I will go back to my place.’ He returns and sleeps again, and then (getting up), he raises his head to find his riding animal standing beside him.
[Saheeh Al-Bukhaari, Hadeeth No. 320, Vol. 8]
Source : The Book Of Repentance : Chapter 1 – Exhortation for At-Tauba (the repentance) and to be pleased for it. Al-Lulu Wal-Marjan, Compiled by : Fuwad Abdul-Baqi, Translated by : Dr. Muhammad Muhsin Khan
1039. Aboo Salama narrated that there was a dispute between him and some people (about a piece of land). When he told Aaisha (radhi Allaahu anha) about it, she said,
O Aboo Salama! Avoid taking the land unjustly, for the Prophet (Sallallaahu Alaihi Wasallam) said, ‘Whoever usurps even one span of the land of somebody, his neck will be encircled with the seven earths
[Saheeh Al-Bukhari, Hadeeth No. 633, Vol.3]
Source : The Book of Al-Musaaqat – Chapter 30 – Prohibition of oppression and taking other’s land by force etc. Al-Lulu Wal-Marjan,Compiled by : Fuwad Abdul-Baqi,Translated by : Dr. Muhammad Muhsin Khan
The heart is healthy ONLY when it is functioning contrast to its desires. In other words, desires are the sickness of the heart and opposing them is the cure.
Ibn al-Qayyim, Sins & their Punishments