It is often said only sincere tawbah can result in major sins being forgiven, and all those virtues that mention all sins are forgiven only refer to minor sins.
Please cite authentic Hadiths, that the Fuqaha have used to confirm this.
In principle, Allah Ta’ala can forgive whenever He wishes.
However, as you have mentioned, the Scholars generally state that for forgiveness from major sins one needs to engage in formal repentance.
The deeds mentioned in various Hadiths that promise forgiveness apply to minor sins. These deeds do not wipe out the major sins. For that one must make tawbah.
Hafiz Ibn Rajab (rahimahullah) writes:
‘The majority of the scholars state that these deeds only expiate the minor sins. The proof for this is in Sahih Muslim in the Hadith of Sayyiduna Abu Hurayrah (radiyallahu’anhu) that Rasulullah (sallallahu’alayhi wasallam) said: ‘The five Salahs, and one to Jumu’ah to the next as well as one Ramadan to the next expiate the sins between them as long as the major sins are avoided.’
(Lataiful Ma’arif, pg. 372 and Sahih Muslim, Hadith: 551)
This Hadith clearly states that the major sins are excluded.
Hafiz Ibn Hajar (rahimahullah) writes:
‘This [Hadith in Sahih Muslim] proves that only the minor sins are wiped away. Therefore all other general narrations (which do not specify only the minor sins as being expiated] will be understood in this light.
(Also see Fathul Bari, Hadith: 883, also see Hadith: 159)
And Allah Ta’ala Knows best,
Answered by: Moulana Muhammad Abasoomar