SAHABA IN ISLAM OR COMPANIONS OF PROPHET MUHAMMAD ﷺ
Sahaba are the companions (includes both Male and Female) of Prophet Muhammad (May Allah honour Him and grant Him peace) during His life time.
Sahabi is someone who saw or met Prophet Muhammad (May Allah honour Him and grant Him peace) and believed in him as well as died as a Muslim. Those that saw him but held off believing in him until after his passing are not considered Sahaba but Tabaeen. Sahabi is used to refer a single companion of Prophet and the word Sahaba is used for plural ie, more than one companion of Prophet. 
It is compulsory for every Muslim whether male or female to believe in Sahaba (companions of Prophet Muhammad(May Allah honour Him and grant Him peace) Allah (Glory be to Him) has set a criteria for the believers to follow them as mentioned in various places of the Qur'aan So if we Muslims want to be on right path then its compulsory for us to follow the companions of Prophet Muhammad(May Allah honour Him and grant Him peace) as mentioned in Qur’an. Surah Baqrah 2:137, Surah Nisa 4:115 Surah Taubah 9:100, Surah Fath 48:29 and Surah Bayyinah 98:8. 
1. As Sabiqoon Al Awaloon:The People,who became Muslim before Badr are called As Sabiqoon Al Awaloon. They are further categorized as
They are considered as best of the Ummah, followed by Tabaeen and Taba tabaeen. Narrated by Abdullah ® and Aisha ® in other narration: The Prophet (May Allah honour Him and grant Him peace) said, "The best people are those of my generation, and then those who will come after them (the next generation), and then those who will come after them (i.e. the next generation), and then after them, there will come people whose witness will precede their oaths, and whose oaths will precede their witness." Sahih Al Bukhari Vol 5:3, Vol 8: 437 and Sahih Al Muslim 6159. 
It was narrated from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do not revile my companions, for by the One in Whose hand is my soul, if one of you were to spend the equivalent of Uhud in gold, it would not amount to a mudd of one of them, or half of that.” Narrated by al-Bukhaari (3673) and Muslim (2540).
Ibn Mas’ood (may Allaah be pleased with him) said: Allaah looked into the hearts of His slaves, and He saw that the heart of Muhammad (peace and blessings of Allaah be upon him) was the best of people’s hearts, so He chose him for Himself and sent him with His message. Then He looked into the hearts of His slaves after the heart of Muhammad, and He found that the hearts of his companions were the best of people’s hearts, so He made them the supporters of His Prophet, who fought for His religion. So whatever the Muslims think is good, is good before Allaah, and whatever they think is bad, is bad before Allaah. Narrated by Ahmad in al-Musnad (1/379). The scholars of hadeeth said: Its isnaad is hasan. 
Al-Imam Ahmad bin Hanbal [d.241h], may Allah have mercy on him said, "From the fundamental principles of sticking to the Sunnah of the Messenger of Allah, prayers and peace upon him, is sticking to [and understanding] the Sunnah however the Companions of the of the Messenger of Allah, prayers and peace upon him, stuck to [and understood] the Sunnah...".
All this should suffice as evidence that the correct understanding of Islam is that of the first three generations and all those that follow their path, in truth. There is no disagreement among Muslim scholars that the best generations of Islam are to be followed, that the interpretation of the Qur'aan and Sunnah they agreed upon is regarded as the correct one, and that we are to approach the Deen (way of life) in the manner they approached it. We are obliged to follow them, and that means, first and foremost, to have the same creed as they did, no deviations, no additions and no deletions. We also have to approach `ibadah in the same way, no innovations, no additions and no deletions. We take all of the Sunnah and refer all disagreements to Allah (Glory be to Him) and His Messenger, as Allah commanded us in the Qur'an.Surah Nisa4:59. To follow the Sahaba does not only mean to have the same understanding of the prescripts of belief as they did. That belief must be manifested in our actions and to follow the Sahaba also means to possess their other characteristics, some of which have been identified by our scholars as:
The Sahaba presented every action according to the scales of the Sharee`ah (Islamic Law), they used to remember and think a lot about death, they were forgiving to those who wronged them in any way, they had a great respect for the honour of other Muslims, for whom they desired only good, they were mindful of their prayers, they used to put the Hereafter before this Dunya (world), they realized that they could not thank Allah enough and they stayed away from the sinful and their gatherings. Allah (Glory be to Him), The Exalted, most appropriately describes them: "Muhammad is the Messenger of Allah, and those who are with him (the Companions) are severe against disbelievers, and merciful among themselves. You see them bowing and falling down prostrate (in prayer), seeking Bounty from Allah and (His) Good Pleasure. The mark of them (i.e. of their faith) is no their faces (foreheads) from the traces of (their) prostration (during prayers)." Qur’an.Surah Fatah 48:29. We ask Allah (Glory be to Him) to enable us to learn about the lives of the Sahaba and to make our lives resemble theirs. For, as Ibn Tahmiya (May Allah have Mercy on Him) said, "Whoever will read their biographies with understanding and insight, and will come to know the rewards bestowed by Allah (Glory be to Him) upon them, he will certainly realise that these are the best among humans after the Prophets (Peace be upon them All). Neither there has been anyone like them nor will there be."