Seven Great Sins

Ibne Mehboob has mentioned in his 'Sahih' that he and his companions had written a letter to Imam Reza (a.s.) enquiring about the number of the Greater Sins. Also the method of determining their "greatness". The respected Imam (a.s.) replied thus:
"The Greater Sins are those, the performers of which have been promised (Hell) fire. If any believer abstains from these or repents for the same Allah will forgive these sins. There are seven such sins, which have been promised (Divine) punishment.

1. To kill one whose murder is prohibited.
2. To disobey parents.
3. To accept usury.
4. To return to ignorance after migration (Hijrat).
5. To accuse a chaste woman of adultery.
6. To consume wrongfully the property of orphans.
7. To flee from the battlefield.
(Wasaaelush Shia). 

Abu Samit has narrated from Imam as-Sadiq (a.s.) that he said:
The Greater Sins are;
1. To associate others (attribute partners) to Allah.
2. Killing anyone whose killing is prohibited by Shariat.
3. Wrongfully acquiring the property of orphans.
4. To disobey parents.
5. To accuse falsely a chaste woman of adultery.
6. To flee (cowardly) from the battlefield.
7. To deny any of the obligations of religion promulgated by Allah. 

Abdur Rehman Ibne Katheer has narrated from the same Masoom (a.s.) that he said:
"Not acknowledging the rights of us (Ahle Bayt) is a Greater sin."

Abi Khadija has quoted a tradition that:
"To attribute falsehood to the Holy Prophet (s.a.w.s.) and the Holy Imams (a.s.) is counted among the Greater Sins." 

Sadooq (r.a.) has quoted that: "To deprive anyone of his rights (What he rightfully deserves) by not mentioning him in one's will is a Greater sin." 

The book Kanzul Ummal has mentioned in a tradition:
"Shedding blood in the precincts of the Holy Ka'ba is a Greater sin."

This is because Allah has ordained it to be a protected sanctuary.

 - Greater Sins, Vol. 1