The Royal (Peel) Commission of 1938

The field in which the Jewish National Home was to be established was understood, at the time of the Balfour Declaration, to be the whole of historic Palestine, and the Zionists were seriously disappointed when Trans-Jordan was cut away from that field under Article 25 of the Palestine Mandate (eg June 1922). This was done, as has been seen, in obedience to the McMahon Pledge, which was antecedent to the Balfour Declaration.

Source: The Palestine Royal (Peel) Commission Report Cmd. 5479 (pg 38) )** (have in PDF)