There is no denying the fact that there exist many differences between the Shia and Ahle Tasannun. Both sects claim to be true followers of the Holy Prophet (peace be upon him and his progeny) and his Sunnah (practice). One of the sources of Prophetic teachings and practices for both sects is through authentic narrations and traditions of the Holy Prophet (peace be upon him and his progeny) which were transmitted through his companions (Ashaab). However, this is one of the points of contention and distinction. There is a vast difference between both sects when it comes to the reliability and trustworthiness of companions. So let us try and find out the real definition of a “Sahaabi” (companion) of the Holy Prophet (peace be upon him and his progeny).”
Ahle Tasannun definition
In the preface of his book al-Isaabah, vol. 1, p. 10, the first section concerning “The Definition of the companion (sahaabi), Ibn Hajar writes:
“The companion (sahaabi) is the one who has met the Prophet (peace be on him and his progeny), believed in him and died as a Muslim. It will apply for all those met him, whether for a short time or for a longer duration, whether he narrated from him or not, whether he accompanied him in his wars or not, one who saw him with his eyes even if he did not get his company, and even the one who could not see him due to some defect like blindness.”
He also quotes al-Tabari and Ibn Asaakir, vide their chain of narrators, who quoted Saif from Abu Uthman from Khalid and Obaadah, who said: “The leaders were from among the companions (sahaabah), unless they could not find anyone to take charge.” 
In another narration stated by al-Tabari, quoting Saif, he said: “The Caliph Umar did not digress from putting into command the Sahaabah if he found among them someone who could replace him in his war. If there had been no such person, he would choose one from among the good Taabe‘een (i.e. those who had seen the companions but not the Prophet – peace be on him and his progeny). None of the apostates could ever hope to obtain command of the army…” 
Two problems with these two narrations from Al-Tabari
- The issue with the above narrations from Al-Tabari is that the source of both is Saif who was notorious for fabrication (of traditions) and being an atheist. 
- The second narration of Umar not appointing anyone except a Sahaabi as a commander of the army is even more unconvincing because the author of Al-Aghaani says that: “Imrah al-Qais adopted Islam at the hands of Umar, who immediately made him a commander, although he had not yet performed a single unit (of prayers) for Allah.” 
Consequences of accepting this definition
- Only meeting the Holy Prophet (peace be on him and his progeny), believing in him and dying as a Muslim are sufficient for any person to be called a Sahaabi
- Tenure spent with the Holy Prophet (peace be upon him and his progeny) is not important
- Anyone who sees him even if it is just before his death, accepts Islam and then himself dies as a Muslim will also be called a Sahaabi.
- A person who accepted Islam, later deviated, reverted just before the martyrdom of Holy Prophet (peace be upon him and his progeny) and then continued to remain a Muslim will also be called a Sahaabi
- Anyone who has not learnt his teachings or narrated his traditions to others but meets the above mentioned criteria is also a Sahaabi
- Actions of the person are also not taken into account as to whether the person is a good-doer or sinner
Sahaabi as defined by the Shias
The Arabic equivalent for companion is saahib (صَاحِب) and its plural is ashaab (اَصْحَاب), sihaab (صِحَاب) and sahaabah (صَحَابَۃ). Saahib means al-Mu’aashir (الْمُعَاشِر) i.e. ‘with whom one socialises’. Another meaning is al-Mulaazim (الْمُلَازِم) which means ‘an inseparable friend’.
It is not used except for the one whose company is for a long duration.
Companionship demands prolonged friendship. 
Merit in accepting the Shia approach
- The Shias consider only that person to be a companion (Sahaabi) who has spent a long enough duration with the Messenger of Allah (peace be upon him and his progeny)
- This definition also demands a person to be on good terms with the Messenger of Allah (peace be upon him and his progeny)
- It means exercising precaution before accepting anyone as a Sahaabi and not a blanket rule where everyone is viewed with the same lens irrespective of their character and actions
- When it comes to narrating traditions, more the precaution, lesser are the chances of error because error in narrating Prophetic traditions will lead to error in beliefs, actions and the entire religion per se.
Al-Suhbah (companionship) happens between two things and implies that it should be annexed to another noun such as: “يَا صَاحِبَيِ السِّجْنِ O you the two companions of the prison” or “أَصْحَابُ مُوْسٰى the companions of Moosa”. During the days of the Holy Prophet (peace be upon him and his progeny), they used to say: “companion(s) of the Prophet” i.e. the word “companion” was annexed to “the Prophet” or in the case of “the companions of the Suffah”, both attributed to some noun (person or place). In those days, the words saahib and ashaab were not used for the companions of the Prophet (peace be upon him and his progeny) alone.
Later on, the followers of the so-called Caliphate School called only a companion of the Holy Prophet (peace be upon him and his progeny) as a sahaabi and ashaab. Therefore, this was one of the nomenclature of Muslims and those of the jurists.
The clear demarcation between the two sects with regards to the definition of a Sahaabi clearly proves that the Ahle Tasannun, by way of their casual and over the top definition, accept Prophetic traditions and practices (Sunnah) from anyone whom they regard as a Sahaabi. As a result, there are a lot of contradictions and confusions in their practices. They assume many of their practices are as per the Prophetic teachings but it is not so.
On the other hand, the Shias exercise more caution and do not accept narrations from anyone and everyone. It is this cautious and intellectual approach while studying and researching the Prophetic traditions which sets them apart from other Muslims.
One thing which is evident and irrefutable is that both approaches definitely cannot be right. Ultimately, everyone is free to choose the path they want on account of the intellect, power and freewill which Allah, the Almighty, has granted because the Holy Quran states in Surah al-Qasas (28): verse 55
وَ إِذَا سَمِعُوْا اللَّغْوَ أَعْرَضُوْا عَنْهُ وَ قَالُوْا لَنَا أَعْمَالُنَا وَ لَكُمْ أَعْمَالُكُمْ سَلامٌ عَلَيْكُمْ لَا نَبْتَغِي الْجَاهِلِيْنَ
“And when they hear idle talk they turn aside from
it and say: We shall have our deeds and you shall have your deeds; peace be on
you, we do not desire the ignorant.”
 Al-Tabari, Eu Ed. vol. 1, p. 2151
 Ibid, pp. 2457-2458
 As per Saif’s biography in the book Abdullah Ibn Sabaa, vol. 1
 Al-Aghaani, Sasi Ed. vol. 14, p. 158
 Look up Lisaan al-Arab under the root s-h-b (صحب)
 Al-Mufradaat by Raaghib al-Isfahaani under the root s-h-b (صحب)
 Surah Yusuf (12): Verse 39
 Surah al-Sho’ara (26): verse 61