Here are some verses on repentance:
But whosoever repents after his crime and does righteous good deeds (by obeying Allah), then verily, Allah will pardon him (accept his repentance). Verily, Allah is OftForgiving, Most Merciful. ( Al-Maeda, Chapter #5, Verse #39)
Allah accepts only the repentance of those who do evil in ignorance and foolishness and repent soon afterwards; it is they to whom Allah will forgive and Allah is Ever AllKnower, AllWise. ( An-Nisa, Chapter #4, Verse #17)
Verily, those who disbelieved after their Belief and then went on increasing in their disbelief (i.e. disbelief in the Quran and in Prophet Muhammad SAW) - never will their repentance be accepted (because they repent only by their tongues and not from their hearts). And they are those who are astray.
( Aal-e-Imran, Chapter #3, Verse #90)
And of no effect is the repentance of those who continue to do evil deeds until death faces one of them and he says: "Now I repent;" nor of those who die while they are disbelievers. For them We have prepared a painful torment.
(An-Nisa, Chapter #4, Verse #18)
Will they not repent to Allah and ask His Forgiveness? For Allah is OftForgiving, Most Merciful. ( Al-Maeda, Chapter #5, Verse #74)