The fundamentals of the religion

It is narrated from Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Three things are among the root and foundation of the religion: (first) that you pray the Friday prayer behind every righteous and sinful (imam or ruler); (second) that the funeral prayer be offered for whoever dies from the people of the qiblah; and (third) that jihad be continued under the leadership of whoever the caliph may be. You will certainly receive your reward for this."
[Takhrij: This narration is in Musnad Ishaq bin Rahwayh: 474; its chain contains a narrator named Muhammad bin Ulwan, who is majhul (unknown), though the matters mentioned in the hadith are established by the agreed beliefs of Ahl al-Sunnah and by other authentic hadith].

It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever deems lawful the things it has made unlawful has not (truly) believed in the Qur'an."
Abd bin Humayd narrated it from Abu Bakr. Muhammad bin Yazid bin Sinan differed from his father in the chain of this narration and narrated it with the chain Ata from Mujahid from Suhayb, which Imam Ibn Adi mentioned.

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "A man said to his (religious) brother: 'La yaghfirullahu lak' (Allah will not forgive you), and it was said to him (by Allah Almighty): 'Bal laka la yaghfirullah' (Rather, (the truth is that) it is you whom Allah will not forgive)."
Sahih (authentic).

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that a man put his foot on the neck of another man while he was in prostration. He (the one prostrating) said (in anger): "Have you put your foot on my neck while I am in prostration? By Allah! Allah will never forgive you." Then he said: "He swore an oath concerning Allah Almighty (that Allah would not forgive so-and-so), so Allah forgave him (the other man)."
Imam Musaddad recorded this hadith and all its narrators are thiqat (trustworthy).