The people of Paradise will not have any regrets except for ..
The Prophet sallallaahu ‘alayhi wa sallam said:
“The people of Paradise will not have any regrets except for those moments in which they were not engaged in the dhikr (remembrance) of Allaah.“
[Saheeh, related by lbnus-Sunnee in 'Aml al-Yawma wal-Laylah (no.3). Refer to Saheehul-Jaami' no.5446]
the Prophet sallallaahu ‘alayhi wa sallam said:
“There is no time in which the son of Aadam does not remember Allaah in it, except that it will be a source of regret for him on the Day of Judgement”
[Hasan, related by Abu Nu'aym in al-Hiliyatul-Awliyaa (51361-362). Refer to Saheehul-Jaami' no.5720]
Further reading: http://abdurrahman.org/zikr/polishinghearts.html