All praise is due to Allah, and peace and blessings be upon the Messenger of Allah.
Conscience may encourage a person to appreciate good and dislike evil, but it is not sufficient by itself to serve as a complete moral guide or inner guardian. It can be influenced by one's environment, customs, and personal desires, causing it to weaken or even become distorted until a person begins to approve of falsehood and reject the truth.
In Islam, the true inner guardian is faith in Allah, awareness that He is always watching, the sound natural disposition (fitrah) with which Allah created mankind, and the guidance brought by the Divine Revelation.
No.
Conscience alone is not an infallible source of morality. This is why standards of right and wrong differ from one person and society to another. A Muslim refers back to the Qur'an and the Sunnah, because they are the true criterion that distinguishes truth from falsehood.
For this reason, one person may feel guilty about something while another sees the same act as perfectly normal. This shows that conscience is influenced by a person's upbringing and surroundings.
The greatest protection against sin is a believer's certainty that Allah sees, hears, and will hold every person accountable. Allah says:
"Does he not know that Allah sees?"
(Qur'an 96:14)
The stronger a person's faith becomes, the more conscious they are of Allah's constant watchfulness, and the more they avoid sins—even when no one else is watching.
Allah created human beings with a natural disposition (fitrah) that inclines them toward loving truth and disliking falsehood. This natural disposition helps a person recognize goodness in a general sense, while Divine Revelation explains the details of what is lawful and unlawful.
Thus, the light of the fitrah is joined with the light of faith, as Allah says:
"Light upon light. Allah guides to His light whom He wills."
(Qur'an 24:35)
Conscience may remind a person of goodness, but it is neither the perfect inner guardian nor the ultimate source of morality. The true guardian is faith in Allah, awareness of His constant watchfulness, adherence to the guidance of the Qur'an and the Sunnah, together with the sound natural disposition upon which Allah created mankind.
And Allah knows best.