Reference for Taanit 48:5
אמר רב מרי ברה דבת שמואל אנא הוה קאימנא אגודא דנהר פפא חזאי למלאכי דאידמו למלחי דקא מייתי חלא ומלונהו לארבי והוה קמחא דסמידא אתו כולי עלמא למיזבן אמר להו מהא לא תיזבנון דמעשה נסים הוא למחר אתיין ארבי דחיטי דפרזינא
As soon as he had taken off one shoe rain fell. As he was about to take off the other Elijah appeared and said to him: The Holy One, Blessed be He, said, if you will take off the other shoe I will lay waste the world.<span class="x" onmousemove="('comment',' He should not weary God with any further prayers as He had already answered his prayer.');"><sup>9</sup></span> R'Mari the son of the daughter of Samuel related: Once I was standing on the bank of the river Papa<span class="x" onmousemove="('comment',' A tributary of the Euphrates. V. Obermeyer, p. 227.');"><sup>10</sup></span> and I saw angels in the guise of sailors who brought sand and loaded ships with it and it turned into fine flour. When the people came to purchase [it] I called out to them: Do not buy this because it resulted from a miracle.