The Greater Sins ( Gunahane Kabeera)

Musa bin Ja’far said, ‘Once, Amr bin Ubayd came to Abu Abdullah (as-Sadiq) (a.s). When he offered greeting and took a seat, he recited this Qur’anic verse, (And those who shun the great sins and indecencies) and kept silent.
Abu Abdullah (a.s) said to him, ‘What made you keep silent?’
Amr said, ‘I like to know the great sins from the Book of Allah the Almighty.’
Abu Abdullah (a.s) said, ‘O yes Amr! The greatest of sins is polytheism. Allah says, (Surely whoever associates (others) with Allah, then Allah has forbidden to him the Paradise) and being desperate of the mercy of Allah because Allah says, (…surely none despairs of Allah's mercy except the unbelieving people) and then the feeling safe from the sudden punishment of Allah because Allah says, (But none feels secure from Allah's plan except the people who shall perish). From the great sins there are also undutifulness to parents because Allah has considered an undutiful one to his parents as arrogant and unblessed, and killing a person that Allah has forbidden except for a just cause because Allah says, (And whoever kills a believer intentionally, his punishment is hell; he shall abide in it) and defaming a married woman because Allah says, (Surely those who accuse chaste believing women, who are unaware (of the evil), are cursed in this world and the hereafter, and they shall have a grievous chastisement) and eating the properties of the orphans for Allah says, (As for) those who swallow the property of the orphans unjustly, surely they only swallow fire into their bellies and they shall enter burning fire) and the fleeing from jihad (sacred war) for Allah says, ( And whoever shall turn his back to them on that day, unless he turn aside for the sake of fighting or withdraws to a company, then he, indeed, becomes deserving of Allah's wrath, and his abode is hell; and an evil destination shall it be) and eating usury because Allah says, (Those who devour usury will not stand except as stand one whom the Satan by his touch Hath driven to madness) and magic because Allah says, (…they taught men sorcery…then men learned from these two, magic…and surely they do know that he who bought it therein will have no (happy) portion in the Hereafter) and adultery because Allah says, (…and (who) do not commit fornication, and he who does this shall find a requital of sin. The punishment shall be doubled to him on the day of resurrection, and he shall abide therein in abasement) and the perjury oath because Allah says, ((As for) those who take a small price for the covenant of Allah and their own oaths, surely they shall have no portion in the hereafter) and embezzlement because Allah says, (Whoso embezzles will bring what he embezzled with him on the Day of Resurrection) and preventing the obligatory zakat because Allah says, (On the day when it shall be heated in the fire of hell, then their foreheads and their sides and their backs shall be branded with it) and false testimony and the concealing of a testimony because Allah says, (…and do not conceal testimony, and whoever conceals it, his heart is surely sinful) and drinking alcohol because Allah has prohibited it, worshipping the idles, giving up the prayer intentionally or giving up any other obligation that Allah has imposed because the messenger of Allah says, ‘Whoever gives up the prayer intendedly will be free from the trust of Allah and His messenger’ and breaking the promise and the rapture of the relations with the kin because Allah says, (And those who break the covenant of Allah after its confirmation and cut asunder that which Allah has ordered to be joined and make mischief in the land; (as for) those, upon them shall be curse and they shall have the evil abode). 
Then Amr went out weeping loudly and saying, ‘Perishes he who follows his own opinion and disputes with you on virtue and knowledge…’( Bihar al-Anwar, vol. 12 p.128-129.)