Parents

Narrated Abu Bakr (RA): Allah's Messenger (ﷺ) said, "Shall I inform you of the biggest of the great sins?" They said, "Yes, O Allah's Apostle (ﷺ)!" He said, "To join partners in worship with Allah, and to be undutiful to one's parents."

Sahih al-Bukhari 6273, Book 79, Hadith 47