Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
bayhaqi:8578Abū Bakr b. al-Ḥārith al-Faqīh > Abū Muḥammad b. Ḥayyān al-Aṣbahānī > Ibrāhīm b. Muḥammad b. al-Ḥasan > Abū ʿĀmir Mūsá b. ʿĀmir > al-Walīd b. Muslim > Saʿīd / Ibn Bashīr > ʿUbaydullāh b. ʿUmar > Nāfiʿ > Ibn ʿUmar > ʿUmar b. al-Khaṭṭāb Nadhar

[Machine] To stay in seclusion in the mosque and observe fasting, the Messenger of Allah ﷺ was asked by someone who had converted to Islam. He commanded him to fulfill his vow, mentioning the vow of fasting along with seclusion. This strange incident was narrated exclusively by Sa'id bin Bashir, on the authority of 'Ubaidullah. And Allah knows best.  

البيهقي:٨٥٧٨وَأَخْبَرَنَا أَبُو بَكْرِ بْنُ الْحَارِثِ الْفَقِيهُ أنبأ أَبُو مُحَمَّدِ بْنُ حَيَّانَ الْأَصْبَهَانِيُّ ثنا إِبْرَاهِيمُ بْنُ مُحَمَّدِ بْنِ الْحَسَنِ ثنا أَبُو عَامِرٍ مُوسَى بْنُ عَامِرٍ ثنا الْوَلِيدُ بْنُ مُسْلِمٍ أَخْبَرَنِي سَعِيدُ يَعْنِي ابْنَ بَشِيرٍ عَنْ عُبَيْدِ اللهِ بْنِ عُمَرَ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ أَنَّ عُمَرَ بْنَ الْخَطَّابِ ؓ نَذَرَ

أَنْ يَعْتَكِفَ فِي الشِّرْكِ وَلَيَصُومَنَّ فَسَأَلَ رَسُولَ اللهِ ﷺ بَعْدَ إِسْلَامِهِ فَأَمَرَهُ أَنْ يَفِيَ بِنَذْرِهِ ذِكْرُ نَذْرِ الصَّوْمِ مَعَ الِاعْتِكَافِ غَرِيبٌ تَفَرَّدَ بِهِ سَعِيدُ بْنُ بَشِيرٍ عَنْ عُبَيْدِ اللهِ وَاللهُ أَعْلَمُ