Thul-Hijjah 14, 1329
1) I have, indeed, read this hadith on page 111 of Volume One of Ahmed's Musnad and ascertained the reliability of his sources and found them to be the most reliable authorities. Then I researched his avenues avenues in narrating this hadith, and I found them to be sequential: each one of them supports the other; therefore, I have contented myself to believe in its contents.
2) But you do not rely on an authentic hadith that deals with the issue of succession unless it is sequentially narrated [mutawatir], for succession, according to your Shi`a philosophy, is one of the roots of religion, and this hadith cannot be considered as "mutawatir" (consecutively reported) and, therefore, it cannot be relied upon.
3) It may be said that `Ali is the successor of the Prophet (pbuh) in his own Household alone; so, where is the text that testifies to his succession among the general public?
4) This hadith may even be revoked, since the Prophet has refrained from publicly supporting the gist thereof. Because of this, the companions found no reason why they should not swear the oath of allegiance to the three righteous caliphs, may Allah be pleased with them.