Sunan Ibn Majah Book 33, Hadith 159
the Messenger of Allah (saas) said: 'I seek the forgiveness of Allah and repent to Him one hundred times each day.'
"We used to count that the Messenger of Allah (ﷺ) said one hundred times in a gathering: 'Rabbighfirli wa tub `alayya innaka Antat-Tawwabur-Rahim (O Allah forgive me and accept my repentance, for You are the Accepter of repentance, the Most Merciful).'"
his grandfather said: "The Messenger of Allah (saas) said: 'I seek the forgivenenss of Allah and repent to Him seventy times each day.'"