Al-Kāfi

Hadith 817
oaths-vows
4- مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ حَمَّادِ بْنِ عِيسَى عَنْ حُسَيْنٍ الْقَلانِسِيِّ أَوْ بَعْضِ أَصْحَابِهِ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ لِلْعَبْدِ أَنْ يَسْتَثْنِيَ فِي الْيَمِينِ فِيمَا بَيْنَهُ وَبَيْنَ أَرْبَعِينَ يَوْماً إِذَا نَسِيَ.
4. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from Hammad ibn ‘Isa from Husayn al- Qalanisiy or certain persons of his people who has narrated the following: “Abu ‘Abd Allah (a.s.), has said, ‘A servant (of Allah) can make the exception up to forty days if he forgets.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī