The grave of Diya'u'llah was desecrated despite Abdul Baha forgiving him.

Baha’u'llah’s other son, Mirza Diya’u’llah, was a vacillating person who wavered in his allegiance to the Centre of the Covenant; he was easily manipulated and became a willing tool in the hands of Mirza Muhammad-‘Ali. He lived in the Mansion of Bahji along with the rest of the family, all of whom were affected by the spirit of Covenant-breaking. Mirza Diya’u’llah died in 1898 not very long after the passing of Baha’u’llah. He did not live to take an effective part in all the hostile activities which his brother was conducting against ‘Abdu’l-Baha. After his death ‘Abdu’l-Baha said that He had forgiven him.

(The Covenant of Baha’u’llah by Adib Taherzadeh, p 165)