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.
tirmidhi:469Maḥmūd b. Ghaylān > ʿAbd al-Razzāq > Ibn Jurayj > Sulaymān b. Mūsá > Nāfiʿ > Ibn ʿUmar

Messenger of Allah said: "When Fajr begins, then every Salat of the night and Al-Witr have gone, so perform Al-Witr before Fajr begins."  

الترمذي:٤٦٩حَدَّثَنَا مَحْمُودُ بْنُ غَيْلاَنَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ أَخْبَرَنَا ابْنُ جُرَيْجٍ عَنْ سُلَيْمَانَ بْنِ مُوسَى عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا طَلَعَ الْفَجْرُ فَقَدْ ذَهَبَ كُلُّ صَلاَةِ اللَّيْلِ وَالْوِتْرُ فَأَوْتِرُوا قَبْلَ طُلُوعِ الْفَجْرِ  

قَالَ أَبُو عِيسَى وَسُلَيْمَانُ بْنُ مُوسَى قَدْ تَفَرَّدَ بِهِ عَلَى هَذَا اللَّفْظِ وَرُوِيَ عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ لاَ وِتْرَ بَعْدَ صَلاَةِ الصُّبْحِ وَهُوَ قَوْلُ غَيْرِ وَاحِدٍ مِنْ أَهْلِ الْعِلْمِ وَبِهِ يَقُولُ الشَّافِعِيُّ وَأَحْمَدُ وَإِسْحَاقُ لاَ يَرَوْنَ الْوِتْرَ بَعْدَ صَلاَةِ الصُّبْحِ

See similar narrations below:

Collected by Suyūṭī
suyuti:2162a

Messenger of Allah said: "When Fajr begins, then every Salat of the night and Al-Witr have gone, so perform Al-Witr before Fajr begins." (Using translation from Tirmidhī 469)   

السيوطي:٢١٦٢a

"إذا طَلَعَ الفجْرُ فَقَدْ ذَهَبَ كُلُّ صلاة اللَّيلِ والوتْرُ، فأوْترُوا قَبْلَ طُلوع الْفَجْرِ".  

[عب] عبد الرازق [ت] الترمذي ومحمد بن نصر عن ابن عمر