Abu Hurayra used to ascribe what he heard of prophetic traditions from any one to the Prophet (S) as if he himself had heard them from the Prophet (S) directly without looking for any evidence of certainty.
If you were in doubt of that, would you please notice his saying: “Prophet Muhammad (S) said to his uncle Abu Talib: “Say: there is no god but Allah (swt). I will witness it for you in the Day of Resurrection.” His uncle said: “I am afraid that Quraysh may blame me for that.”
It was certain for all that Abu Talib had died ten years before Abu Hurayra came to Hijaz. So where were the Prophet (S) and his uncle talking in this tradition that Abu Hurayra narrated as if he had seen with his own eyes and heard them with his own ears?
He said: “When Allah (swt) revealed to the Prophet (S) (And warn your nearest relations), he stood up and said: “O people of Quraysh, I don't substitute for you near Allah (swt) (in the Day of Resurrection).
All of the jurisprudents and scholars agreed unanimously that this Qur'anic verse was revealed to the Prophet (S) in the beginning of the Islamic mission and before declaring it in Mecca, where Abu Hurayra was still worshipping his idols in Yemen. He came to Hijaz twenty years after the revelation of this verse. He narrated this tradition as if he had been among the attendants to see the Prophet (S) with his eyes standing up and hear him with his ears warning his tribe.
He said: “The Prophet (S) prayed in his prayer saying: “O Allah (swt), save Salama bin Hisham, save al-Waleed bin al-Waleed, save Ayyash bin Abu Rabee'a. O Allah (swt) save the oppressed believers (who were held back by the polytheists in order not to emigrate with the others from Mecca to Medina).
This happened seven years before Abu Hurayra came to Hijaz and became a Muslim. He narrated it as if he had been with the Prophet (S) when he was praying.
If Abu Jahl really had said that, it would have been twenty years before Abu Hurayra came from Yemen and became a Muslim. He narrated it as if he had seen and heard what happened.
Where was he from the combat of ar-Rajee' and its leader Aassim bin Thabit al-Ansari, who was martyred in it to tell of it as if he had seen everything? It happened in the month of Safar the fourth year of hijra, three years before Abu Hurayra came to Hijaz and became a Muslim.
Any one, who inquired the manner of Abu Hurayra in narrating traditions, would know that he was just as what we said. These few traditions were enough to prove that.
Abu Hurayra himself confessed that. When he narrated that the Prophet (S) had said: “Whoever was impure when it dawned, he was not to fast.” Aa'isha and Um Salama denied it. He accused al-Fadhl bin al-Abbas, who was dead then, of saying that. He said that he had heard it from al-Fadhl and had not heard it from the Prophet (S). Anyhow he confessed, whether it was true or false, that he ascribed to the Prophet (S) what he had heard from others.
If you say: what of it if he ascribed to the Prophet (S) a tradition that he had heard from another one?
We say: it does not matter, but the tradition must not be considered as true tradition unless all the series of narrators would be known and proved to be trusty.
That is to say the honesty of the narrator must be proved as condition for the tradition to be true. The tradition must not be considered as true one if the narrator was unknown.
In a word, many of Abu Hurayra's traditions were such that it could not be depended upon. They mixed with his true traditions that made us avoid them all according to the rule of suspicions.
 It was mentioned by Muslim in his Sahih, vol.1, chapter of “Faith”, pg.31.
 It was mentioned by al-Bukhari in his Sahih, vol.2 chapter on Wasaaya, pg.86; by Muslim in his Sahih and Ahmed in his Musnad. We mentioned it in the previous chapter and commented on it.
 Refer to al-Bukhari’s Sahih, vol,2 section on asking the lord to defeat infidels, pg.105.
 Muslim’s Sahih, vol.2, pg.467.
 Al-Bukhari’s Sahih, vol.2 chapter of Jihad, pg.117.
 Fajrul Islam (the dawn of Islam), pg.262.
 Refer to Al-Bukhari’s Sahih, vol.1 section on waking up in state of Junub while fasting , pg.225.