This is an absolute necessity, that we ask Allah while believing that He will respond.
The Prophet (peace be upon him) said, ‘none of you should say: 'O Allah! forgive me if You wish,’ or 'bestow Your mercy on me if You wish,’ or 'provide me with means of subsistence if You wish,’ but he should be firm in his request, for Allah does what He wills and nobody can force Him (to do anything). [Sahih al-Bukhari 97: 103]
The Prophet (peace be upon him) also said, 'ask Allah when you are sure of His response, and remember that Allah does not accept the dua of the unmindful and neglectful heart.’ [Al-Tirmidhi and al-Hakim, sahih al-Jami: 245]