Is the questioner sinful for not advising his father, who delays the Fajr prayer beyond its time, and how can he advise him given the presence of shyness?

What the father does by missing prayers until their time expires without an excuse is a grave sin that necessitates repentance. He must be advised gently and kindly, as an fulfillment of the duty of enjoining good and forbidding evil and offering sincere advice. Neither shyness nor the assumption that he is in a state of major ritual impurity (janabah) should prevent advising him.

Advice can be direct or indirect, such as having him listen to lectures or gifting him booklets about prayer, all while being gentle in the advice; because the matter of one's father is not like that of others. Ahmad said: "He enjoins good upon his parents and forbids evil from them. If he sees his father doing something he dislikes, he teaches him without harshness or offense, and he does not use strong language with him, otherwise he leaves it. The father is not like a stranger."

Failure to advise when possible may lead to sin due to a shortcoming in the duty of advice, and it may be considered disobedience (uquq); because part of filial piety is advising him to obey Allah.