Why Abubakr Denied Fadak - The Hidden Motive

The famous Sunni scholar Ibn Abil-Hadid Mu’tazali has 

said about his discourse with a fellow Sunni scholar concerning the truthfulness of the Prophet’s daughter: 

“I asked Ali Ibn Fareqi, a distinguished teacher of Madrassat-al-Gharbiyya of Baghdad: "Was Fatema truthful in making the claim ?" (regarding her patrimony of the orchard of Fadak, which the Caliph had seized on the pretext that Prophets do not leave inheritance – despite the explicit words of the Qur’an that Solomon inherited David)

He answered: "Yes!"

I said: "Did Abu Bakr know that she was a truthful lady?"

Again he answered: "Yes."

I then asked: "Then why did the Caliph not give back to her that which she was entitled to?"

At that moment the teacher smiled and said with great dignity: 

"If he had accepted her word on that day and had returned Fadak to her on account of her being a truthful lady and without asking for any witnesses, she could very well use this position for the benefit of her husband on the following day by saying, “my husband, Ali is entitled to the caliphate.” And then the Caliph would have been obliged to surrender the caliphate to Ali on account of his having acknowledged her to be a truthful lady. However, in order to obviate any such claim or dispute he deprived her of her undisputed right!"

Reference : Sharh-i Nahjul Balaghah by Ibn Abil Hadid, page 284.