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:21191[Chain 1] Abū ʿAbdullāh al-Ḥāfiẓ > Abū al-Walīd al-Faqīh > al-Ḥasan b. Sufyān > Abū Bakr [Chain 2] And ʾNbʾ Abū al-Walīd > Muḥammad b. Aḥmad b. Zuhayr > ʿAbdullāh b. Hāshim > Wakīʿ > Ismāʿīl al-Azraq > al-Shaʿbī

[Machine] The testimony of one witness is not valid until there are two witnesses. The Sheikh, may Allah have mercy on him, said that Imam Shafi'i brought up the topic of testimony in cases of boundaries, and we have mentioned the reports and traditions about it in the book of boundaries and the book of theft.  

البيهقي:٢١١٩١أَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ أنبأ أَبُو الْوَلِيدِ الْفَقِيهُ ثنا الْحَسَنُ بْنُ سُفْيَانَ ثنا أَبُو بَكْرٍ ح قَالَ وَأنبأ أَبُو الْوَلِيدِ ثنا مُحَمَّدُ بْنُ أَحْمَدَ بْنِ زُهَيْرٍ ثنا عَبْدُ اللهِ بْنُ هَاشِمٍ قَالَا ثنا وَكِيعٌ عَنْ إِسْمَاعِيلَ الْأَزْرَقِ عَنِ الشَّعْبِيِّ قَالَ

لَا تَجُوزُ شَهَادَةٌ الَشَاهِدٍ عَلَى الشَّاهِدِ حَتَّى يَكُونَا اثْنَيْنِ قَالَ الشَّيْخُ رَحِمَهُ اللهُ قَدْ أَعَادَ الشَّافِعِيُّ رَحِمَهُ اللهُ هَهُنَا بَابَ الشَّهَادَةِ عَلَى الْحُدُودِ وَقَدْ ذَكَرْنَا الْأَخْبَارَ وَالْآثَارَ فِيهِ فِي كِتَابِ الْحُدُودِ وَكِتَابِ السَّرِقَةِ