Sunan Ibn Majah Book 34, Hadith 25
"The Messenger of Allah (saas) said: 'There is no supplication that a person can say that is better than: Allahumma inni as'aluka al-mu'afah fid-dunya wal-akhirah (O Allah, I ask You for Al-Mu'afah in this world and in the Hereafter).'"
"O Messenger of Allah, what do you think I should say in my supplication, if I come upon Laylatul-Qadr?" He said: "Say: 'Allahumma innaka 'afuwwun tuhibbul-'afwa, fa'fu 'anni (O Allah, You are Forgiving and love forgiveness, so forgive me).'"
the Messenger of Allah (saas) said: "May Allah have mercy on us and on our brother of 'Ad." (i.e., Prophet Hud alay-salaam).