וַיְהִ֣י כְעָבְרָ֗ם וְאֵ֨לִיָּ֜הוּ אָמַ֤ר אֶל־אֱלִישָׁע֙ שְׁאַל֙ מָ֣ה אֶֽעֱשֶׂה־לָּ֔ךְ בְּטֶ֖רֶם אֶלָּקַ֣ח מֵעִמָּ֑ךְ וַיֹּ֣אמֶר אֱלִישָׁ֔ע וִֽיהִי־נָ֛א פִּֽי־שְׁנַ֥יִם בְּרוּחֲךָ֖ אֵלָֽי׃
And it came to pass, when they were gone over, that Elijah said unto Elisha: ‘Ask what I shall do for thee, before I am taken from thee.’ And Elisha said: ‘I pray thee, let a double portion of thy spirit be upon me.’
Read kabbalistic (mystical) interpretation of II Kings 2:9: and classical mystical sources.