Asking for Divine Pardon
Imam Amir ul Mu'mineen ‘Ali (‘a) said: "Perfume yourself with penitence so that the stench of your sins do not disgrace you."
Bihar-ul-Anwar, vol. 6, p. 22
Imam Amir ul Mu'mineen ‘Ali (‘a) taught someone to seek Allah in invocation in brief by saying: "Praise is (only) Allah's for every blessing; and I ask Him for all goodness; and I take refuge in Allah from all vices; and, I seek Allah's forgiveness for all sins."
Bihar-ul-Anwar, vol. 94, p. 242
Imam al-Baqir (‘a) said that the Holy Prophet (S) was once asked about the best servants and he replied:
"They are such that: when they do good, they are cheerful about it; when they do wrong, they seek forgiveness; when they are granted (something), they are thankful; when they are involved in a difficulty, they show patience; and when they become angry (with someone), they pardon."
Khisal by Saduq, p. 317
Imam as-Sadiq (‘a) said: "When a believing Muslim frequently asks Allah for forgiveness, his record (of deeds) will ascend while it will be glowing."
Makarim-ul-Akhlaq, p. 313