2 Corinthians 12:7-10 (NKJV)
The Thorn in the Flesh
7 And lest I should be exalted above measure by the abundance of the revelations, a thorn in the flesh was given to me, a messenger of Satan to [a]buffet me, lest I be exalted above measure. 8 Concerning this thing I pleaded with the Lord three times that it might depart from me. 9 And He said to me, “My grace is sufficient for you, for My strength is made perfect in weakness.” Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me. 10 Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ’s sake. For when I am weak, then I am strong.
Daniel 9:1-3 (NKJV)
Daniel’s Prayer for the People
9 In the first year of Darius the son of Ahasuerus, of the lineage of the Medes, who was made king over the realm of the Chaldeans— 2 in the first year of his reign I, Daniel, understood by the books the number of the years specified by the word of the Lord through Jeremiah the prophet, that He would accomplish seventy years in the desolations of Jerusalem.
3 Then I set my face toward the Lord God to make request by prayer and supplications, with fasting, sackcloth, and ashes.
Luke 18:1-8 (NKJV)
The Parable of the Persistent Widow
18 Then He spoke a parable to them, that men always ought to pray and not lose heart, 2 saying: “There was in a certain city a judge who did not fear God nor [a]regard man. 3 Now there was a widow in that city; and she came to him, saying, [b]‘Get justice for me from my adversary.’4 And he would not for a while; but afterward he said within himself, ‘Though I do not fear God nor regard man, 5 yet because this widow troubles me I will [c]avenge her, lest by her continual coming she weary me.’ ”
6 Then the Lord said, “Hear what the unjust judge said. 7 And shall God not avenge His own elect who cry out day and night to Him, though He bears long with them? 8 I tell you that He will avenge them speedily. Nevertheless, when the Son of Man comes, will He really find faith on the earth?”