This is also a proven true hadith in the Sunni sources, Imam Tirmidhi also wrote this hadith. This hadith clearly says that “Ali is from me and I am from Ali. No one can convey on my behalf except myself or Ali.”
Please check this link to read this hadith from Nissaie.
The Holy Prophet (pbuh) said it about Imam Ali when Abu Baker asked the Holy Prophet to recite the verses of Surah Taubah against the pagons at the time of Hajj. Jibrail came to the Holy Prophet that Allah wants to give this reponsibilty to Imam Ali. The Holy Prophet got back the reponsibility from Abu Baker to announce the verses of Quran on the Prophet's behalf and gave it to Imam Ali (as).
We can also note that Allah(swt) and his Prophet (pbuh) did not give Abu Bakar the responsibility to recite some verses of Surah Taubah, how can it be possible for Abu Bakar to have authority to interpret the whole Quran for the Muslim Ummah?
English Translation:
Sayyidina Hubshi ibn Junadah reported that Allah’s Messenger (SAW) said,
“All is from me and I from Ali and none shall represent me except myself or Ali.”
Imam Tirmidhi graded this as Hassan Sahih.