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.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
nasai-kubra:4655 – ʿAlī b. Ḥujr > Ibn al-Mubārak > Yūnus

[Machine] It is permissible if they both agree for one of them to decide over the other.  

الكبرى للنسائي:٤٦٥٥ – أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ قَالَ أَخْبَرَنَا ابْنُ الْمُبَارَكِ عَنْ يُونُسَ عَنِ الزُّهْرِيِّ فِي عَبْدَيْنِ مُتَفَاوِضَيْنِ كَاتَبَ أَحَدُهُمَا قَالَ

جَائِزٌ إِذَا كَانَا مُتَفَاوِضَيْنِ يَقْضِي أَحَدُهُمَا عَلَى الْآخَرِ  

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Collected by Nasāʾī
nasai:3938 – ʿAlī b. Ḥujr > Ibn al-Mubārak > Yūnus

"One of them may cover for the other if they were partners."  

النسائي:٣٩٣٨ – أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ قَالَ أَنْبَأَنَا ابْنُ الْمُبَارَكِ عَنْ يُونُسَ

عَنِ الزُّهْرِيِّ فِي عَبْدَيْنِ مُتَفَاوِضَيْنِ كَاتَبَ أَحَدُهُمَا قَالَ جَائِزٌ إِذَا كَانَا مُتَفَاوِضَيْنِ يَقْضِي أَحَدُهُمَا عَنِ الآخَرِ