Article1, Section 6

Short Version -- This is a summary of the important issues covered in this section of the U.S. Constitution. 

• Members of Congress receive a salary.
• Members of Congress cannot be arrested in the House or Senate chambers.
• Members of Congress cannot be prosecuted for things said or written in connection with their duties.
• Members of Congress cannot hold a federal office during their term of office.
• Members of Congress cannot be appointed to a post created during their tenure.
• Members of Congress cannot be appointed to a post whose salary has been increased during their tenure.

Long Version -- This is the text of the Actual U.S. Constitution. 

The Senators and Representatives shall receive a compensation for their services, to be ascertained by law, and paid out of the treasury of the United States. They shall in all cases, except treason, felony and breach of the peace, be privileged from arrest during their attendance at the session of their respective Houses, and in going to and returning from the same; and for any speech or debate in either House, they shall not be questioned in any other place. 

No Senator or Representative shall, during the time for which he was elected, be appointed to any civil office under the authority of the United States, which shall have been created, or the emoluments whereof shall have been increased during such time: and no person holding any office under the United States, shall be a member of either House during his continuance in office.