Daniel 6
(7) The royal administrators, prefects, satraps, advisers and governors have all agreed that the king should issue an edict and enforce the decree that anyone who prays to any god or man during the next thirty days, except to you, O king, shall be thrown into the lions' den.
(8) Now, O king, issue the decree and put it in writing so that it cannot be altered--in accordance with the laws of the Medes and Persians, which cannot be repealed."
(9) So King Darius put the decree in writing.
(10) Now when Daniel learned that the decree had been published, he went home to his upstairs room where the windows opened toward Jerusalem.[this would be in plain view of anyone passing by his home]. Three times a day he got down on his knees and prayed, giving thanks to his God, just as he had done before.
(11) Then these men went as a group and found Daniel praying and asking God for help.
Jesus did not command his followers to pray in closets. He taught them how to pray (do not chant) and the spirit in which to pray (humility):
Luke 18
1 Then Jesus told his disciples a parable to show them that they should always pray and not give up.
(10) [In a parable, Jesus said] two men went up to the temple to pray, one a Pharisee and the other a tax collector. (11) The Pharisee stood up and prayed about himself: `God, I thank you that I am not like other men--robbers, evildoers, adulterers--or even like this tax collector. (12) I fast twice a week and give a tenth of all I get.' (13) "But the tax collector stood at a distance. He would not even look up to heaven, but beat his breast and said, `God, have mercy on me, a sinner.' (14) "I tell you that this man, rather than the other, went home justified before God. For everyone who exalts himself will be humbled, and he who humbles himself will be exalted."
Acts 1
13 When they arrived, they went upstairs to the room where they were staying. Those present were Peter, John, James and Andrew; Philip and Thomas, Bartholomew and Matthew; James son of Alphaeus and Simon the Zealot, and Judas son of James. (14) They all joined together constantly in prayer, along with the women and Mary the mother of Jesus, and with his brothers.
It is not a commandment to pray alone, in a room. Rather, a reminder that God looks at our intent and heart when we pray. If our intention was as the Pharisees (to gain attention, esteem, status, etc.) then our prayer is worthless, meaningless, and putrid to God. In fact, He turns His face from that type of “prayer.” However, if our spirit comes before God in humility, and is not self-seeking and self-serving, it is a pleasant aroma to Him and He will hear our prayers.