He said: Abul Hasan Ali b. Muhammad b. Hubaish al-Katib reported to me from al- Hasan b. Ali al-Zafarani, who reported from Ibrahim b. Muhammad al-Thaqafi, who reported from al-Masoodi, who reported from Yahya b. SALIm al-Abdi, who reported from Maysarah, from al-Minhal b. Amru, from Zarr b. Hubaish who said:
Once, ALI BIN ABI TALIB (ASWS), passed by riding the PROPHET's (SAWW) mule and Salman was present among the people.
So Salman - may ALLAH (SWT) bless him with mercy, said: "(O people)! do you not rise to detain him and ask him questions? By ALLAH (SWT), Who split the grain and created the breathing creatures, no one but he (i.e. ALI (ASWS) ) will inform you about the secrets of your PROPHET (SAWW).
Indeed, he is the most learned about this earth and its chief element on which it rests. If you miss him, you will miss the knowledge and deny the people (its benefit)."
(Ref: Al-Amali Shaikh Mufeed The Seventeenth Assembly Hadees No. 2)