A brother of mine aged 24 years, died without having ever performed a single Salah (Prayer) in his entire life,
but he might have fasted for one month in his life. Furthermore, he suffered from an addiction to Khamr (intoxicants), Zina (sexual intercourse outside marriage), theft, and he died in a state of drunkenness after his car crashed into a tree. Now, what is the ruling on asking forgiveness for him by his parents?
If the condition of your brother during his lifetime until his death was as you mentioned, then it is not permissible to whoever knew his manners to ask forgiveness for him, for he went under the realm of Kufr (disbelief) by abandoning Salah, as the Prophet (peace be upon him) said,
Between a servant and Shirk (associating others with Allah in His Divinity or worship) and Kufr (disbelief) is abandoning Salah.
Related by Imam
Muslim in his Sahih,
and his saying,
The covenant that distinguishes between us and them (the disbelievers) is Salah. Anyone who abandons it has committed Kufr.
Ahmad and the Compilers of Sunan with an authentic chain of narration, and there are other proofs in this regard.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.