Why would God send a deceitful spirit? 1 Kings 22:19-28
19 Micaiah continued, “Therefore hear the word of the Lord: I saw the Lord sitting on his throne with all the multitudes of heaven standing around him on his right and on his left. 20 And the Lord said, ‘Who will entice Ahab into attacking Ramoth Gilead and going to his death there?’
“One suggested this, and another that. 21 Finally, a spirit came forward, stood before the Lord and said, ‘I will entice him.’
22 “‘By what means?’ the Lord asked.
“‘I will go out and be a deceiving spirit in the mouths of all his prophets,’ he said.
“‘You will succeed in enticing him,’ said the Lord. ‘Go and do it.’
23 “So now the Lord has put a deceiving spirit in the mouths of all these prophets of yours. The Lord has decreed disaster for you.”
24 Then Zedekiah son of Kenaanah went up and slapped Micaiah in the face. “Which way did the spirit from[a] the Lord go when he went from me to speak to you?” he asked.
25 Micaiah replied, “You will find out on the day you go to hide in an inner room.”
26 The king of Israel then ordered, “Take Micaiah and send him back to Amon the ruler of the city and to Joash the king’s son 27 and say, ‘This is what the king says: Put this fellow in prison and give him nothing but bread and water until I return safely.’”
28 Micaiah declared, “If you ever return safely, the Lord has not spoken through me.” Then he added, “Mark my words, all you people!”

So God sends a spirit enticing Ahab in order to attack Ramoth Gilead. If I may dare ask, why does God feel the need to send a deceiving spirit? Would this not go against the Commandments God has given? And why was such a spirit even within the close proximity in the presence of the Lord in the first place? I wish to know how to reconciling this text with others.
Regarding your question, if it is a matter of deceit or not - consider the original context. 

First you should read the whole chapter: 1 Kings 22 

The subject has to do with truth, amazingly. 


  13 The messenger who went to call Micaiah said to him, Behold now, the
  prophets unanimously declare good to the king. Let your answer, I pray
  you, be like theirs, and say what is good.
  
  14 But Micaiah said, As the Lord lives, I will speak what the Lord
  says to me.


The king demands to hear the truth.


  16 And the king said to him, How many times must I charge you to tell
  me nothing but the truth in the name of the Lord?


So the prophet tells the truth.

Then there is the part you mention where God asks "who will go fool Ahab" and a spirit says "I'll be a deceptive spirit in his prophets..." and that is agreed upon.

And thus the prophet summarizes:


  23 So the Lord has put a lying spirit in the mouths of all these
  prophets; and the Lord has spoken evil concerning you.


Notice too - what God said was distinctly different than what the lying spirit said. 

So you can see that although there was indeed deception, God revealed the truth (he cannot lie, and he is the "revealer of secrets") but as usual Ahab follows his own self-convenient thinking and heart as many do. 

This is similar to what is said here:

Deuteronomy 13:1-3


  If a prophet arises among you, or a dreamer of dreams, and gives you a
  sign or a wonder,
  
  2 And the sign or the wonder he foretells to you comes to pass, and if
  he says, Let us go after other gods—gods you have not known—and let us
  serve them,
  
  3 You shall not listen to the words of that prophet or to that dreamer
  of dreams. For the Lord your God is testing you to know whether you
  love the Lord your God with all your [mind and] heart and with your
  entire being.


Again - with the fore-knowledge of such things, you actually have the truth of the matter ahead of time so the seeming deception is irrelevant - unless one's lying heart wishes to believe it. God has not lied. (Romans 3:4)



Similar passages:
2 Samuel 15:31 


  31 David was told, Ahithophel [your counselor] is among the
  conspirators with Absalom. David said, O Lord, I pray You, turn
  Ahithophel’s counsel into foolishness.


Job 5:13


  13 He catches the [so-called] wise in their own trickiness, and the
  counsel of the schemers is brought to a quick end.