In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Indeed, Allaah described His faithful servants who were true in their faith, deeds, Jihad and covenants.

لَيْسَ الْبِرَّ أَنْ تُوَلُّوا وُجُوهَكُمْ قِبَلَ الْمَشْرِقِ وَالْمَغْرِبِ وَلَكِنَّ الْبِرَّ مَنْ ءَامَنَ بِاللَّهِ وَالْيَوْمِ الآخِرِ وَالْمَلَائِكَةِ وَالْكِتَابِ وَالنَّبِيِّينَ وَءَاتَى الْمَالَ عَلَى حُبِّهِ ذَوِي الْقُرْبَى وَالْيَتَامَى وَالْمَسَاكِينَ وَابْنَ السَّبِيلِ وَالسَّائِلِينَ وَفِي الرِّقَابِ وَأَقَامَ الصَّلَاةَ وَءَاتَى الزَّكَاةَ وَالْمُوفُونَ بِعَهْدِهِمْ إِذَا عَاهَدُوا وَالصَّابِرِينَ فِي الْبَأْسَاءِ وَالضَّرَّاءِ وَحِينَ الْبَأْسِ أُولَئِكَ الَّذِينَ صَدَقُوا وَأُولَئِكَ هُمُ الْمُتَّقُونَ

It is not Al-Birr (piety, righteousness, and each and every act of obedience to Allah, etc.) that you turn your faces towards east and (or) west (in prayers); but Al-Birr is (the quality of) the one who believes in Allah, the Last Day, the Angels, the Book, the Prophets and gives his wealth, in spite of love for it, to the kinsfolk, to the orphans, and to Al-Masakin (the poor), and to the wayfarer, and to those who ask, and to set slaves free, performs As-Salat (Iqamat-as-Salat), and gives the Zakat, and who fulfill their covenant when they make it, and who are As-Sabirin (the patient ones, etc.) in extreme poverty and ailment (disease) and at the time of fighting (during the battles). Such are the people of the truth and they are Al-Muttaqun (pious). [Surah Al-Baqarah. Aayah 177]

Allaah [The Exalted] said:

مِنَ الْمُؤْمِنِينَ رِجَالٌ صَدَقُوا مَا عَاهَدُوا اللَّهَ عَلَيْهِ فَمِنْهُمْ مَنْ قَضَى نَحْبَهُ وَمِنْهُمْ مَنْ يَنْتَظِرُ وَمَا بَدَّلُوا تَبْدِيلاً

Among the believers are men who have been true to their covenant with Allah [i.e. they have gone out for Jihad (holy fighting), and showed not their backs to the disbelievers], of them some have fulfilled their obligations (i.e. have been martyred), and some of them are still waiting, but they have never changed [i.e. they never proved treacherous to their covenant which they concluded with Allah] in the least. [Surah Al-Ahzaab. Aayah 23]

Allaah [The Exalted] said:

إِنَّمَا الْمُؤْمِنُونَ الَّذِينَ ءَامَنُوا بِاللَّهِ وَرَسُولِهِ ثُمَّ لَمْ يَرْتَابُوا وَجَاهَدُوا بِأَمْوَالِهِمْ وَأَنْفُسِهِمْ فِي سَبِيلِ اللَّهِ أُولَئِكَ هُمُ الصَّادِقُونَ

The believers are only the ones who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. It is those who are the truthful. [Surah Al-Hujuraat. Aayah 15]
And The Exalted [Allaah] stated in praising the poor Muhaajiroon – and all the companions of Muhammad are truthful, there is no difference between the Muhaajiroon and the Ansaar -:

لِلْفُقَرَاءِ الْمُهَاجِرِينَ الَّذِينَ أُخْرِجُوا مِنْ دِيارِهِمْ وَأَمْوَالِهِمْ يَبْتَغُونَ فَضْلاً مِنَ اللَّهِ وَرِضْوَانًا وَيَنْصُرُونَ اللَّهَ وَرَسُولَهُ أُولَئِكَ هُمُ الصَّادِقُونَ

(And there is also a share in this booty) for the poor emigrants, who were expelled from their homes and their property, seeking Bounties from Allah and to please Him. And helping Allah (i.e. helping His religion) and His Messenger (Muhammad). Such are indeed the truthful (to what they say). [Surah Al-Hashar. Aayah 8]

Indeed, Allaah commended Muhammad’s Companions [peace and blessings of Allaah be upon him] and praised them a lot in His decisive Book, and His Messenger [may peace and blessings of Allaah be upon him] praised them with great praise in many hadiths. One the most prominent and manifest qualities of theirs -with which they have been described – is truthfulness- a (quality) without which religion and the worldly affairs cannot be established.

These truthful people and those who inherited their path conveyed to us – with complete truthfulness and trustworthiness- the Book of Allaah through numerous successive unbroken chains of transmission, and the Sunnah of His Messenger through both the authentic narrations that have been transmitted based on successive numerous unbroken chains and those transmitted by one reliable person, including the biography of Allaah’s Messenger [peace and blessings of Allaah be upon him], his Jihad and conquests. The authentic books, the Musannafaat (1), the Jawaami (2) , the Ma’aajim (3), the books of (sound) creed and others are filled with these transmissions, in which the Imaams of Al-Jarh Wat Tadeel (the scholars who are specialised in the science of criticism and commendation) distinguished the authentic narrations from the weak (faulty) narrations, so that the Muslim Ummah is on a straight path, a correct methodology, and a conscious and upright life (based on the Qur’aan, the Sunnah and the understanding of Muhammad’s companions). They conveyed to us the path of the noble companions, their statuses and virtues, which manifestly distinguished from all the other nations of the Prophets and with these (virtues) they became the best of the nations ever raised for humankind. The books regarding the statuses of the companions and their virtues, and other collections of the Sunnah are filled with this. [[End of quote https://www.mimham.net/tan-1308-82 slightly paraphrased]

1: Al-Musannafaat: Books authored on the subject matter of Hadith – mostly contain narrations related to rulings on acts of worship based on Islamic jurisprudence, the different chapters of Islamic jurisprudence, the narrations and verdicts of the Prophet’s companions, their students and the students of their students.

2: Al-Jawaami: First type are the books that gather different types of narrations on the subject matter of creed, rulings, affairs of the heart, manners of eating and drinking, travel, residence, subject matter of tafseer, history, affairs of trials and tribulations, signs of the hour, virtues of the companions etc. Some Imaams who compiled these works and their titles include: Saheeh Al-Bukhaari; Saheeh Muslim; Al-Muwatta; Musnad Ahmad; Sunan An-Nasaa’ee; Sunan Abu Daawud; Sunan At-tirmidhee; Sunan Ibn Maajah; Sunan Ad-Daarimi; Saheeh Ibn Khuzaymah; Saheeh Ibn Hibbaan. Second type are books whose authors intended to gather a large number of Prophetic Ahaadeeth, or gather Ahaadeeth of specific books, or gather different Ahaadeeth in a specific subject matter, such as ‘Jaami-ul Ahaadeeth of As-Suyooti; Jaami-ul usool Fee Ahaadeeth Ar-Rasool of Ibnul Atheer; Silsilah As-Saheehah of Albaanee; Sharh Mushkilah Al-Aathaar of Tahaawi; Al-Musnad Al-Jaami of Nawawi; Nailul Awtaar of Shawkaanee etc.

3: Ma’aajim: Books that contain words (or terms) related to language, a subject matter, the names and levels of scholars etc.