What is the evidence the British supplied gold and guns to the Saudi tribe during the first world war?

During the First World War, the British government supplied gold and guns to the Saudi tribe, led by Abdulaziz bin Abdul Rahman al-Saud, also known as Ibn Saud, as part of their agreements and deals to secure their support against the Ottoman Caliphate. One source for this is the book "The Saudi-British Relationship: The Politics of Diplomacy, Business, and Culture" by Madawi Al-Rasheed, in which she states: "The British government supplied Ibn Saud with gold and guns as part of the 1915 Treaty of Darin, which recognized Saudi control over the territories of Nejd and Hejaz, and promised to support the Saudi state financially in exchange for their support against the Ottoman Empire." Another source is the book "Britain and the Arab Middle East, 1914-1922" by Martyn C. Rady, in which he found: "the British government provided financial and military aid to the Saudi state in exchange for their support against the Ottoman Empire, including supplies of gold and weapons." Additionally, the book "Ibn Saud: The Desert Warrior Who Created Saudi Arabia" by Asher Orkaby, also illustrates the deal between the two parties, the British and the Saudi tribe, and the provision of gold and weapons to the Saudi tribe. These sources argue the British government supplied gold and guns to the Saudi tribe during the First World War as part of their agreements and deals to secure their support against the Ottomans.