Ubaidullah bin Abdullah (narrates this statement of Sayyiduna Abdullah bin Abbas, may Allah be pleased with them): Once I was present with Sayyiduna Umar, may Allah be pleased with him, and we were discussing about prayer. During this, Sayyiduna Abdur Rahman bin Auf, may Allah be pleased with him, arrived. He said: Shall I not narrate to you the hadith which I heard from the Messenger of Allah, peace and blessings be upon him? I heard the Messenger of Allah, peace and blessings be upon him, say: "When you have doubt about any deficiency during prayer, then continue performing the prayer until that doubt becomes about an addition."