Musnad Abu Ya'la al-Mawsili 150:145

'Abd al-A'la narrated to us, Mu'ammar narrated to us, he said: I heard Layth narrating from Shahr ibn Hawshab that a man said to 'A'ishah: "Indeed, one of us speaks to himself about something; if he were to speak of it, his Hereafter would be gone, and if it were to be revealed about him, he would be killed." She said: "Then she said 'Allahu Akbar' three times, then she said: 'The Messenger of Allah (ﷺ) was asked about it, so he said 'Allahu Akbar' three times, then he said: "The believer is only tested by this."'"