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
bayhaqi:2580 – Abū Bakr b. al-Ḥārith al-Faqīh > Abū Muḥammad b. Ḥayyān > Ibrāhīm b. Muḥammad b. al-Ḥasan > Abū ʿĀmir Mūsá b. ʿĀmir > al-Walīd / Ibn Muslim > Mālik And Ibn Jurayj > Nāfiʿ > Ibn ʿUmar

[Machine] That the imam raises his head indicates that he has completed that unit of prayer.  

البيهقي:٢٥٨٠ – وَأَخْبَرَنَا أَبُو بَكْرِ بْنُ الْحَارِثِ الْفَقِيهُ أنبأ أَبُو مُحَمَّدِ بْنُ حَيَّانَ ثنا إِبْرَاهِيمُ بْنُ مُحَمَّدِ بْنِ الْحَسَنِ ثنا أَبُو عَامِرٍ مُوسَى بْنُ عَامِرٍ ثنا الْوَلِيدُ يَعْنِي ابْنَ مُسْلِمٍ أَخْبَرَنِي مَالِكٌ وَابْنُ جُرَيْجٍ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ أَنَّهُ كَانَ يَقُولُ مَنْ أَدْرَكَ الْإِمَامَ رَاكِعًا فَرَكَعَ قَبْلَ

أَنْ يَرْفَعَ الْإِمَامُ رَأْسَهُ فَقَدْ أَدْرَكَ تِلْكَ الرَّكْعَةَ  

See similar narrations below:

Collected by Bayhaqī
bayhaqi:2582 – Mālik > Balaghah > ʿAbdullāh b. ʿUmar And Zayd b. Thābit Kānā Yaqūlān Man Adrak al-Rakʿah Qabl

[Machine] That the imam raises his head means he has completed the prostration.  

البيهقي:٢٥٨٢ – قَالَ وَحَدَّثَنَا مَالِكٌ أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللهِ بْنَ عُمَرَ وَزَيْدَ بْنَ ثَابِتٍ كَانَا يَقُولَانِ مَنْ أَدْرَكَ الرَّكْعَةَ قَبْلَ

أَنْ يَرْفَعَ الْإِمَامُ رَأْسَهُ فَقَدْ أَدْرَكَ السَّجْدَةَ