This authentic hadith is narrated in mass in both Sunni and Shia literature in many wordings, see one of those wordings from Sunni literature Sunni below.
Source: Musnad al-Imam Ahmed bin Hanbal, Vol. 35, Pg. 512, Hadith. 21654
عَنْ زَيْدِ بْنِ ثَابِتٍ ، قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: إِنِّي تَارِكٌ فِيكُمْ خَلِيفَتَيْنِ: كِتَاب اللهِ ، حَبْلٌ مَمْدُودٌ مَا بَيْنَ السَّمَاءِ وَالْأَرْضِ ، أَوْ مَا بَيْنَ السَّمَاءِ إِلَى الْأَرْضِ ، وَعِتْرَتِي أَهْلُ بَيْتِي ، وَإِنَّهُمَا لَنْ يَتَفَرَّقَا حَتَّى يَرِدَا عَلَيَّ الْحَوْضَ جميعاً
On the authority of Zayd bin Thabit, he said, the Prophet (saw) said: “I am leaving behind among you, two successors (Caliphs). The Book of Allah (swt) and My AhlulBayt (house hold). And know, that these two will never separate until they both reach me at the pond.”
Footnote: Hadith is Saheeh (Authentic) at its core, except for the section that says that they will never separate until they both reach me at the pond.