In the last ten nights of Ramadhan, and during the odd nights of it even more so, it is recommended that one say the following supplication a lot:
Allahumma innaka `afuwwun tuhibbul `afwa fa`fu `annee
“O Allah! Verily, you are the Oft-Pardoning, You love to pardon, so pardon me.”
This is due to what Imam Ahmad recorded from Aishah that she said “O Messenger of Allah! If I find the Night of Al-Qadr what should I say?” He (saws) replied,
Say : “O Allah! Verily You are the Oft-Pardoning, You love to pardon, so pardon me.”
Print out the Laylatul Qadr supplication (pdf). Refer to it as you need to .
At-Tirmidhi, An-Nasai and Ibn Majah have all recorded this Hadith . At-Tirmdhi said “This Hadith is Hasan Sahih” . [Tahfat Al-Ahwadhi 9:495, An-Nasai in Al-Kurba 6:218, and Ibn Majah 2:1265]
Al-Hakim recorded it in his Mustadrak (with a different chain of narration) and he said that it is authentic according to the criterial of the two Shaykhs (Al-Bukhari and Muslim).
[Al-Hakim 1:530] An Nasai also recorded it. [An-Nasai in Al-Kubra 6:219]