Sahih al-Bukhari Book 78, Hadith 8
Allah's Messenger (ﷺ) mentioned the greatest sins or he was asked about the greatest sins. He said, "To join
partners in worship with Allah; to kill a soul which Allah has forbidden to kill; and to be undutiful or
unkind to one's parents." The Prophet (ﷺ) added, "Shall I inform you of the biggest of the great sins? That
is the forged statement or the false witness." Shu`ba (the sub-narrator) states that most probably the
Prophet said, "the false witness."
Allah's Messenger (ﷺ) said thrice, "Shall I not inform you of the biggest of the great sins?" We said, "Yes, O Allah's Messenger (ﷺ)" He said, "To join partners in worship with Allah: to be undutiful to one's parents." The Prophet (ﷺ) sat up after he had been reclining and added, "And I warn you against giving forged statement and a false witness; I warn you against giving a forged statement and a false witness." The Prophet kept on saying that warning till we thought that he would not stop.
My mother came to me, hoping (for my favor) during the lifetime of the Prophet. I asked the Prophet, "May I treat her kindly?" He replied, "Yes." Ibn 'Uyaina said, "Then Allah revealed: 'Allah forbids you not with regards to those who fought not against you because of religion, and drove you not out from your homes, that you should show them kindness and deal justly with them.'.......(60.8)