What is the Biblical basis that prayer is sufficient as a way to recognize truth?

In John 14:6, we read:

Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

But to follow Jesus and to find truth and life is exactly the process of sanctification.

Now, what is prayer?

The answer is probably best viewed from the perspective of the Jews, and therefore of Jesus Christ, who taught us the Lord's Prayer.

To a Jew, a prayer time is a time of self-judgement.

Source: for example, visit the site https://www.chabad.org/library/article_cdo/aid/682090/jewish/The-Meaning-of-Prayer.htm

The Hebrew for “prayer” is tephillah. According to NAS Exhaustive Concordance, it comes from the verb, palal that means “to intervene, interpose”, or as indicated by Brown-Driver-Briggs, “to arbitrate, judge, intercede.” Its reflective verb is lehitpalal, “to judge oneself”. Thus, a prayer time should be a time to examine ourselves carefully, critically and sincerely, knowing that we are all sinners and fall short of God’s glorious standards (Romans 3:23):

For all have sinned, and come short of the glory of God;

Since we cannot possibly meet God’s expectations, we do not deserve His blessings and favors. Therefore, we humble ourselves before Him and confess our sins in our prayers. Psalms 51 and 69 come to mind as some of King David’s most significant prayers that are unparalleled in their long, sincere and careful examination of thoughts and feelings. It is only after first carefully, critically and sincerely examining ourselves that we can partake in sanctification with the help of the Holy Spirit.

It is from this Jewish perspective of what a prayer should be that we can fully understand the Lord’s Prayer – why we begin by exalting God's name when we say Our Father in heaven, holy be your name, humble ourselves before Him when we say forgive us our sins, as we forgive those who sinned against us, and then request the Father not to bring us to the test but deliver us from evil, which is exactly meant for our sanctification.

Prayer is necessary, but not sufficient for acquiring all truth. It is, however, sufficient for acquiring some truth.

The Bible goes to great lengths to describe which means of communication with God are permitted and which are forbidden. For example, consulting the dead, using mediums, and practicing witchcraft and sorcery are forbidden. Other means are permitted, and some means are regarded as superior.

The Book of Job offers considerable insight into how God communicates with humanity. It catalogues most of the major means of hearing from God:

• Observe God's attributes through nature
• Trust the sayings of elders and wise people
• Pray
• Fast
• Interpret dreams and visions
• Learn from suffering
• Listen to the prophets
• Direct inspiration from the Holy Spirit
• Marvel at God's miracles
• Accept the intercession of angels
• Theophany: hear directly from God

It leaves out two important means of hearing from God:

• Reading the Written Word of God (it didn't exist yet)
• Listening to Jesus speak (He hadn't been born yet)

The book then goes on to show the limitations of each:

• Job and his friends misinterpret nature; God sets them straight in his speech (Job 38-41)
• The Elder and wise men misunderstood God's justice and had some bad advice
• The friends said Job was wicked, so God would ignore his prayers; not true of Job, but often true of many other people. OTOH, God commanded Job to pray for the forgiveness of the friends, and God listened (Job 42:8)
• Isaiah would later teach about the difference between a proud and humble fast (Isaiah 58)
• Eliphaz had a dream, but it was from Satan (Job 4:12-21). Several kings in the Old Testament could not understand their dreams without a prophet to explain it.
• Suffering taught Job much, other people fall away on account of it
• the words of the true prophets are essential for understanding many things; of course there are many false prophets, so you need discernment
• Elihu says that the Holy Spirit working within a person is superior to the advice of the wise and aged (Job 32:6-9)
• Many people saw Jesus' miracles, yet did not believe. (John 14:11)
• The people of Sodom and Gomorrah saw the angels, but tried to abuse them (Genesis 19:5)
• Theophany: Hearing directly from God is unambiguously clear. No problems here!

The upshot of all this is that there are many forms of communication, all useful within their limits, and best corroborated by comparision with the knowledge derived from the others. Prayer is no exception.

Prayer is central to receiving spiritual truths from God since by prayer we humble ourselves to a state where the Holy Spirit works effectively in us.

However, are we able to discern if the answer we receive is from God's Spirit or an evil spirit? God in His wisdom has warned us: "Beloved, do not believe every spirit, but test the spirits, whether they are of God (1 John 4:1)." The spirit that speaks against the Word of God is not from God.

The tempter is well aware of this avenue and uses it frequently. And God permits it, allowing us into these types of trials so that we can be trained to strengthen our discernment. It is written "For Satan himself transforms himself into an angel of light (2 Corinthians 11:14)." Those who place their trust in any and every spirit are liable to be deceived by the enemy and overthrown.