All of the Companions of Allaah’s Messenger are trustworthy based on Allaah’s testifying that for them and because of His praise for them and the praise of His Messenger (صلى الله عليه و سلم) for them.
An-Nawawee said in at-Taqreeb, which As-Suyootee explained in his Tadreeb-ur-Raawee:
“All of the Companions are trustworthy – those who were involved in the afflictions (fitan) and other than them – according to the consensus of the scholars.”
Al-Haafidh Ibn Hajr said in al-lsaabah:
“Ahl-us-Sunnah have unanimously agreed that all of them (the Sahaabah) are trustworthy and no one opposed this except some deviants amongst the innovators.”
This is why there is no harm in not knowing a Companion in a chain of narration. So if a Taabi’ee says: “On the authority of a man who accompanied the Prophet…” this does not affect the report. This is because not knowing the Companions (in the chain) causes no harm since they are all trustworthy.
Al-Khateeb Al-Baghdaadee said in his book al-Kifaayah:
“Every hadeeth that has a chain of narration that is connected between the one who reported it and the Prophet is not to be acted upon until first having affirmed the trustworthiness and reliability of all the narrators (in the chain). It is an obligation to investigate all of their conditions, except for the Sahaabee (Companion) who raises it (or attributes the hadeeth) to the Prophet. This is because the trustworthiness of the Companions is established and well known based on Allaah’s affirming that for them, His informing us of their pure state and His preference of them in the texts of the Qur’aan…”
Then he (rahimahullaah) went on to list some ayaat and ahaadeeth concerning their virtues and said:
“And even if Allaah or His Messenger had not mentioned anything about them from what we just stated now (of their virtues), the condition they were upon of having made Hijrah, fought in Jihaad, of having offered their support, sacrificed their lives and wealth, experienced the killings of their parents and children, of mutually advising for the Religion and having strong Faith and unshakeable certainty, (all of this) would be enough to prove their trustworthiness and enough for one to have firm faith in their honesty and integrity. And it would necessitate the understanding that they are the best from those who receive testimony and approval as to their trustworthiness and reliability from all of the people that will come after them forever and ever.”
Posted from : The Creed of Ahlus-Sunnah wal-Jamaa’ah concerning the Companions – Shaikh ‘Abdul-Muhsin bin Hamad Al-‘Abbaad, al-ibaanah eBook