Another proof is the Prophet’s words—recorded among his authentic supplications that he would recite before concluding the prayer with the salutation—
“O Allah, by Your knowledge of the unseen and Your power over every creature, keep me alive so long as You know that life is better for me, and cause me to die when You know that death is better for me.” 1.

He also heard a man while reciting the tashahhud say, “O Allah, I ask You—O Allah, the One, the Unique, the Self-Sufficient Master who neither begets nor is begotten and to whom none is comparable—to forgive me my sins; indeed, You are the All-Forgiving, the Ever-Merciful.” The Prophet said, “He has been forgiven, he has been forgiven.” 2.

On another occasion the Prophet heard a different man during the tashahhud say, “O Allah, I ask You, for to You belongs all praise; there is no god but You alone with no partner. You are al-Mannān (the Bestower of favors), O Originator of the heavens and the earth, O Possessor of Majesty and Honor, O Ever-Living, O Self-Subsisting. I ask You for Paradise and seek refuge in You from the Fire.” The Prophet then said to his Companions, “Do you know by what he just supplicated?” They replied, “Allah and His Messenger know best.” He said, “By the One in whose hand is my soul, he has called upon Allah by His magnificent Name”—in another wording, “His greatest Name”—“which, when He is invoked with it, He answers, and when He is asked by it, He grants.” 3.

Another evidence is his statement: “Whoever finds his worries mounting should say: ‘O Allah, I am Your servant, son of Your servant, son of Your maid-servant; my forelock is in Your hand; Your decree concerning me is executed, and Your judgment concerning me is just. I ask You by every name that is Yours, which You have named Yourself with, or taught to any of Your creation, or revealed in Your Book, or kept unto Yourself within the knowledge of the unseen…’”