Al-Kāfi

Hadith 1768
night-prayerrepentance
33ـ مُحَمَّدُ بْنُ إِسْمَاعِيلَ عَنِ الْفَضْلِ بْنِ شَاذَانَ عَنْ صَفْوَانَ بْنِ يَحْيَى عَنْ مَنْصُورِ بْنِ حَازِمٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ اسْتَغْفِرِ الله فِي الْوَتْرِ سَبْعِينَ مَرَّةً.
33. Muhammad ibn ’Isma‘il has narrated from al-Fadl ibn Shadhan from Safwan ibn Yahya from Mansur ibn Hazim who has said the following: “Abu ‘Abd Allah (a.s.), has said that in al-Witr, ask forgiveness from Allah seventy times.” (Ahadith 20-34 are best explained in the form of fatwa.)
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī