Sifrei Bamidbar 138

(Bamidbar 27:15) "And Moses spoke to the L-rd to say, etc.": (This is mentioned) to apprise us of the virtues of the righteous, that when they are about to die they put aside their own concerns and occupy themselves with those of the congregation. "to say": What is the intent of this? Moses said to Him: Tell me whether you are appointing leaders for them or not — until the Holy One Blessed be He answered him (Ibid. 18) "Take for yourself Joshua the son of Nun, a man who has spirit in him (viz. 16), and place your hand upon him." R. Eliezer b. Azaryah says: In four places Moses made requests of the Holy One Blessed be He and He responded to them, viz. (Shemot 6:12) "And Moses spoke before the L-rd, to say: The children of Israel did not hearken to me. How, then, will Pharaoh do so? And I am impeded of speech." What is the intent of "to say"? Moses said to him: Apprise me whether or not you will redeem them — until the L-rd granted his request, viz. (Ibid. 7:4) "And I will take out My hosts, My people, the children of Israel, from the land of Egypt." Similarly, (Bamidbar 12:13) "And Moses cried out to the L-rd to say "G-d, I pray You; heal her, I pray you." What is the intent of "to say"? He said before Him: Tell me, I pray You, whether or not You will heal her — until the Holy One Blessed be He answered his question, viz. (Ibid. 14) "Now if her father had spat in her face, would she not be in shame for seven days?" Similarly, (Devarim 3:23) "And I supplicated the L-rd at that time to say": What is the intent of "to say"? He said to Him: Tell me whether or not I will enter the land — until the L-rd answered him, viz. (Ibid. 26) "It is enough for you, etc." Here, too, what is the intent of "to say"? He said to him: Tell me whether or not You are appointing leaders for them — until the L-rd answered him: "Take for yourself Joshua the son of Nun."