Ah, finally i've found these one:
Muhammad Bin Yahya, from Ahmad Bin Muhammad, from Muhammad Bin Khalid, from Sa’d Al-Ashary, (It has been narrated) from Abu Al-Hassan Al-Reza asws, said, ‘I asked him asws about the Fitra, how much should be handed over on behalf of every head, from the wheat, and the barley, and the dates, and the raisins: ‘He asws said: ‘A Sa’a by the Sa’a of the Prophet saww’.
(al-Kafi, Vol. 4, Book of Fasts, Ch. 75, H. 6)
A number of our companions, from Muhammad Bin Isa, from Ali Bin Bilal who said, ‘I wrote to the Imam asws asking him asws about the Fitra and how much should be handed over. So he asws wrote: ‘Six Ratls (unit of measurement) of dates by the Medinite (counting), and that is nine Ratls by the Baghdady (counting)’.
(al-Kafi, Vol. 4, Book of Fasts, Ch. 75, H. 8)
Muhammad Bin Yahya, from Muhammad Bin Ahmad, from Ja’far Bin Ibrahim Bin Muhammad Al-Hamdany, and he was a Pilgrim along with us, said, ‘I wrote to Abu Al Hassan asws upon the hand of my father, ‘May I be sacrificed for you asws! Our companions are differing regarding the Sa’a. Some of them are saying the Fitra is to be by the Medinite Sa’a, and some of them are saying it is by the Iraqi Sa’a’. So he asws wrote to me: ‘The Sa’a is six Ratls by the Medinite (counting), and nine Ratls by the Iraqi (counting)’.
(al-Kafi, Vol. 4, Book of Fasts, Ch. 75, H. 9)
According Imam Reza, one صاع النبوي is 6 Madinan رطل or 9 Iraqi رطل.