The Holy Prophet (S) said: "Do not look at the minuteness of the sin, but see Whom you have sinned against."
Bihar-ul-Anwar, vol. 77, p. 79 & Mustadrak Al-Wasa'il, vol. 11, p. 330
Imam Amir ul Mu'mineen ‘Ali (‘a) said: "If one of you desires to know his standing with Allah he may evaluate his situation in relation to his sins against Allah, such is his worthiness to Allah, the Blessed and Exalted."
Bihar-ul-Anwar, vol. 70, p. 18
Imam as-Sadiq (‘a) addressed a group of people and inquired why they annoyed the Messenger of Allah. Someone asked Imam (‘a) how they did so, and he (‘a) said: "Do you not know that your deeds are reported to him (S)? When he (S) observes a sin against Allah among them, he becomes displeased. Therefore do not hurt the Messenger of Allah but do please him."
Usul al-Kafi, vol. 1, p. 219
Imam Amir ul Mu'mineen ‘Ali (‘a) said: "Lacking forgiveness is the worst of deficiencies and hastening in vengeance is (among) the greatest (of all) sins."
Ghurar-ul-Hikam, p. 235
Asbaq-ibn-Nubatah has narrated from the first Imam, Amir ul Mu'mineen ‘Ali (‘a), who said the Prophet (S) said: "When Allah Almighty and Glorious sends His wrath on a nation and does not punish (them) by it, then; their prices will go up (expensive), their lifetimes will shorten, their merchants will not gain profits, their fruits will not be abundant, their streams will not become brimful, their rain will be withheld from them, and their vicious ones will dominate over them."
Khisal by Saduq, vol. 2, p.360
The summary of this tradition is that if the destructive penalty does not destroy such a nation, they will be inflicted with seven afflictions because of their committing sins.
Imam al-Baqir (‘a), the fifth Imam, said that he found in the book of Amir ul Mu'mineen ‘Ali (‘a) that he has said that the Holy Prophet (S) said: "When adultery appears (abundantly in a society) the (number of) sudden deaths increases; and when there is fraud, Allah takes them in expensiveness and loss. When people stop giving alms tax, the earth holds back its blessings from plants (crops), fruits, mines, and all such things. When they act unjustly according to (divine) ordinances, they have helped injustice and aggression. When they breach (their) promises, the Lord will set their enemies as absolute masters over them. When they break off connections with their kindred, possession of properties will be put in the hands of the wicked. And, when they do not perform enjoining right and forbidding wrong and, also, do not follow the chosen ones of my Ahlul Bayt, Allah will set their vicious ones over them and, in this condition, their good doers utter invocations but they are not responded to."
Safinat-ul-Bihar, vol. 2, p. 630
Imam Amir ul Mu'mineen ‘Ali (‘a) said: "The tears do not dry up save for the hearts being hard, and hearts do not harden but because of the abundance of sins."
Bihar-ul-Anwar, vol. 70, p. 55
Allah, the Exalted, told Prophet David (‘a): "O' David! Give good news to the sinners of My absolute Mercy, which envelops everything (in the world of existence), so as not to grow hopeless of My Mercy; and warn the good doers of the authority of My wrath in order not to be proud of their obedience, for pride causes arrogance which itself is the greatest of all sins."
Al-Ithna 'Ashariyyah, p. 59