Every hadith in which it is stated, "His previous and subsequent sins were forgiven," regarding anyone other than the Prophet (peace and blessings be upon him) is a weak hadith.

The Shaykh : Some scholars said: Know that among the specific attributes of the Messenger (peace and blessings be upon him) is that Allah has forgiven him his previous and subsequent sins. Based on this, every hadith, every hadith that states that whoever does such-and-such will have his previous and subsequent sins forgiven, is a weak hadith, because this is a specific attribute of the Messenger. As for "his previous sins were forgiven," that is common, but "his subsequent sins" is a specific attribute of the Messenger (peace and blessings be upon him) alone. This is a beneficial rule that benefits the student of knowledge: if a hadith comes to you stating that whoever does such-and-such will have his previous and subsequent sins forgiven, know that the phrase "his subsequent sins" is weak and not authentic, because this is a specific attribute of Muhammad (may Allah's prayers and peace be upon him).