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
abudawud:756 – Muḥammad b. Maḥbūb > Ḥafṣ b. Ghiyāth > ʿAbd al-Raḥman b. Isḥāq > Ziyād b. Zayd > Abū Juḥayfah > ʿAlī

AbuJuhayfah said: Ali said that it is a sunnah to place one hand on the other in prayer below the navel.  

أبو داود:٧٥٦ – حَدَّثَنَا مُحَمَّدُ بْنُ مَحْبُوبٍ حَدَّثَنَا حَفْصُ بْنُ غِيَاثٍ عَنْ عَبْدِ الرَّحْمَنِ بْنِ إِسْحَاقَ عَنْ زِيَادِ بْنِ زَيْدٍ عَنْ أَبِي جُحَيْفَةَ أَنَّ عَلِيًّا ؓ قَالَ

السُّنَّةُ وَضْعُ الْكَفِّ عَلَى الْكَفِّ فِي الصَّلاَةِ تَحْتَ السُّرَّةِ  

See similar narrations below:

Collected by Aḥmad
ahmad:875 – ʿAbdullāh > Muḥammad b. Sulaymān al-Asadī Lūwayn > Yaḥyá b. Abū Zāʾidah > ʿAbd al-Raḥman b. Isḥāq > Ziyād b. Zayd al-Suwāʾī > Abū Juḥayfah > ʿAlī

Part of the Sunnah in prayer is to put one hand over the other beneath the navel.  

أحمد:٨٧٥ – حَدَّثَنَا عَبْدُ اللهِ حَدَّثَنَا مُحَمَّدُ بْنُ سُلَيْمَانَ الْأَسَدِيُّ لُوَيْنٌ حَدَّثَنَا يَحْيَى بْنُ أَبِي زَائِدَةَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ إِسْحَاقَ عَنْ زِيَادِ بْنِ زَيْدٍ السُّوَائِيِّ عَنْ أَبِي جُحَيْفَةَ عَنْ عَلِيٍّ قَالَ

إِنَّ مِنَ السُّنَّةِ فِي الصَّلاةِ وَضْعُ الْأَكُفِّ عَلَى الْأَكُفِّ تَحْتَ السُّرَّةِ