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
suyuti:1865a –

that the Messenger of Allah ﷺ said: "If you see those who abuse my Companions, then say: 'May Allah's curse be upon the worst of you.'" (Using translation from Tirmidhī 3866)   

السيوطي:١٨٦٥a –

"إِذَا رأيتُمَ الذِينَ يَسُبُّونَ أَصْحَابي فقولوا: لَعْنَةُ الله علَى شَرِّكم".  

[ت] الترمذي منكر عن ابن عمر

See similar narrations below:

Collected by Tirmidhī, Suyūṭī
tirmidhi:3866 – Abū Bakr Muḥammad b. Nāfiʿ > al-Naḍr b. Ḥammād > Sayf Ibn ʿUmar > ʿUbaydullāh b. ʿUmar > Nāfiʿ > Ibn ʿUmar

that the Messenger of Allah ﷺ said: "If you see those who abuse my Companions, then say: 'May Allah's curse be upon the worst of you.'"  

الترمذي:٣٨٦٦ – حَدَّثَنَا أَبُو بَكْرٍ مُحَمَّدُ بْنُ نَافِعٍ قَالَ حَدَّثَنَا النَّضْرُ بْنُ حَمَّادٍ قَالَ حَدَّثَنَا سَيْفُ ابْنُ عُمَرَ عَنْ عُبَيْدِ اللَّهِ بْنِ عُمَرَ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ قَالَ

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا رَأَيْتُمُ الَّذِينَ يَسُبُّونَ أَصْحَابِي فَقُولُوا لَعْنَةُ اللَّهِ عَلَى شَرِّكُمْ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ مُنْكَرٌ لاَ نَعْرِفُهُ مِنْ حَدِيثِ عُبَيْدِ اللَّهِ بْنِ عُمَرَ إِلاَّ مِنْ هَذَا الْوَجْهِ وَالنَّضْرُ مَجْهُولٌ وَسَيْفٌ مَجْهُولٌ
suyuti:1857a –

that the Messenger of Allah ﷺ said: "If you see those who abuse my Companions, then say: 'May Allah's curse be upon the worst of you.'" (Using translation from Tirmidhī 3866)   

السيوطي:١٨٥٧a –

"إِذَا رأيتُمَ الذين يَسُبُّونَ أصحابي فقولُوا: لَعَنَ اللهُ شَرَّكُمْ" .  

الخطيب في أمالي العلماء، [هب] البيهقى في شعب الإيمان عن ابن عمر