The only Regret in JANNAH:
Mu`adh ibn Jabal (RA) said that the Prophet (SAWS) said:
"The People of Paradise will not regret except one thing alone: the hour that passed them by in which they made no Dhikr (remembrance) of Allah."
Narrated by Bayhaqi in Shu`ab al-iman (1:392 #512-513) and by Tabarani. Haythami in Majma` al-zawa'id (10:74) said that its narrators are all trustworthy (thiqat), while Suyuti declared it hasan in his Jami` al-saghir (#7701).
-Extracted from a long article on Dhikr on sunnah.org