Is it permissible to inform a religious sister that her suitor does not adhere to the Sunnah of the Prophet (peace be upon him), believing that the Holy Quran is sufficient, and is it religiously obligatory to reject him?

Whoever rejects the Sunnah in whole and in detail is a disbeliever, because he thereby contradicts the verses of the Qur'an that command obedience to the Messenger, peace and blessings of Allah be upon him. Whoever claims to act only by the Qur'an cannot know the details of acts of worship such as prayer, zakat, and Hajj, because their details are found in the Sunnah. Rejecting the Sunnah is a rejection of the religion and disbelief in Allah the Almighty. Whoever does that is a disbeliever in the Qur'an, even if he claims to believe in it. It is not permissible to marry off a woman to one who rejects the Sunnah, and the guardian must be informed of this and prevented from doing so if he is the guardian. As for one who rejects an authentic hadith due to a misconception or interpretation, he is not a disbeliever, and he should be advised and shown the truth, and there is no objection to marrying him.