This occurs in Act III. Hale is actually arguing that Proctor be able to hire a lawyer to Danforth. After having witnessed what Hale believes are possibly innocent people be sentenced to death, Hale wants to make sure that what is going on is actually true.
We have textual evidence of this sentiment in the following words of Hale:
I cannot say [Proctor] is an honest man; I know him little. But in all justice, sir, a claim so weighty cannot be argued by a farmer. In God's name, sir, stop here; send him home and let him come again with a lawyer -
This comment of Hale's demonstrates that hale does not believe Proctor is intellectually equipped to handle his own court proceedings. He believes Proctor needs a professional to act on his behalf.
Furthermore, when Hale signs Rebecca Nurse's death warrant, he seems to feel the guilt of damning her excellent moral reputation. John Proctor is no different:
I have this morning signed away the soul of Rebecca Nurse, Your Honor. I'll not conceal it, my hand shakes yet as with a wound! I pray you, sir, this argument let lawyers present to you.
This also demonstrates that Hale's conscience is eating at him. I believe he is worrying about how he will answer to God for his own actions one day.
Hale thinks that Proctor needs a lawyer because he believe that Proctor was telling the truth at first but because he didnt have a lawyer and no one believed him, Proctor start saying he believe in witchcraft.