2 Kings 2:8 (KJV)

And Elijah said unto him, Tarry, I pray thee, here; for the Lord hath sent me to Jordan. And he said, As the Lord liveth, and as thy soul liveth, I will not leave thee. And they two went on.

And fifty men of the sons of the prophets went, and stood to view afar off: and they two stood by Jordan.

And Elijah took his mantle, and wrapped it together, and smote the waters, and they were divided hither and thither, so that they two went over on dry ground.

And it came to pass, when they were gone over, that Elijah said unto Elisha, Ask what I shall do for thee, before I be taken away from thee. And Elisha said, I pray thee, let a double portion of thy spirit be upon me.

And he said, Thou hast asked a hard thing: nevertheless, if thou see me when I am taken from thee, it shall be so unto thee; but if not, it shall not be so.