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:505Abū Bakr Aḥmad b. ʿAlī al-Ḥāfiẓ > Ibrāhīm b. ʿAbdullāh al-Aṣbahānī > Muḥammad b. Isḥāq b. Khuzaymah > Yūsuf b. Mūsá > Jarīr > al-Aʿmash > Abū Sufyān > Jābir

[Machine] The Messenger of Allah ﷺ said, "If one of you intends to perform I'tikaf (spiritual seclusion in a mosque), then he should do so for three days. In this, there is an indication that he orders seeking spiritual seclusion in odd numbers, and the most virtuous odd number is the number one."  

البيهقي:٥٠٥أَخْبَرَنَاهُ أَبُو بَكْرٍ أَحْمَدُ بْنُ عَلِيٍّ الْحَافِظُ ثنا إِبْرَاهِيمُ بْنُ عَبْدِ اللهِ الْأَصْبَهَانِيُّ ثنا مُحَمَّدُ بْنُ إِسْحَاقَ بْنِ خُزَيْمَةَ ثنا يُوسُفُ بْنُ مُوسَى نا جَرِيرٌ عَنِ الْأَعْمَشِ عَنْ أَبِي سُفْيَانَ عَنْ جَابِرٍ قَالَ

قَالَ رَسُولُ اللهِ ﷺ إِذَا اسْتَجْمَرَ أَحَدُكُمْ فَلْيَسْتَجْمِرْ ثَلَاثًا وَفِي هَذَا كَالدَّلَالَةِ عَلَى أَنَّ أَمْرَهُ بِالِاسْتِجْمَارِ وِتْرًا هُوَ الْوِتْرُ الَّذِي يَزِيدُ عَلَى الْوَاحِدِ