Reference on Pople basis set
You should look on Basis set exchange

After you select your basis set of interest, on the bottom left you click "Get References for selected basis", and in this case you obtain (I did it for elements C,H,O):


  References for the basis set
  
  H

## VTZ Valence Triple Zeta: 3 Funct.'s/Valence AO for H,He
Krishnan, R., Binkley, J. S., Seeger, R., Pople, J. A.
Self-consistent molecular orbital methods. XX. A basis set for
        correlated wave functions
J. Chem. Phys., 72, 650-654 (1980)
10.1063/1.438955

## 1P Polarization functions associated with 6-311G for H,He
Krishnan, R., Binkley, J. S., Seeger, R., Pople, J. A.
Self-consistent molecular orbital methods. XX. A basis set for
        correlated wave functions
J. Chem. Phys., 72, 650-654 (1980)
10.1063/1.438955

## Diffuse functions asociated with 31G Hydrogen
Clark, Timothy, Chandrasekhar, Jayaraman, Spitznagel, Günther W.,
        Schleyer, Paul Von Ragué
Efficient diffuse function-augmented basis sets for anion
        calculations. III. The 3-21+G basis set for first-row
        elements, Li-F
J. Comput. Chem., 4, 294-301 (1983)
10.1002/jcc.540040303

  
  C,O

## VTZ Valence Triple Zeta: 3 Funct.'s/Valence AO
Krishnan, R., Binkley, J. S., Seeger, R., Pople, J. A.
Self-consistent molecular orbital methods. XX. A basis set for
        correlated wave functions
J. Chem. Phys., 72, 650-654 (1980)
10.1063/1.438955

## 1P Polarization functions associated with 6-311G
Krishnan, R., Binkley, J. S., Seeger, R., Pople, J. A.
Self-consistent molecular orbital methods. XX. A basis set for
        correlated wave functions
J. Chem. Phys., 72, 650-654 (1980)
10.1063/1.438955

## Diffuse functions asociated with 6-31G
Clark, Timothy, Chandrasekhar, Jayaraman, Spitznagel, Günther W.,
        Schleyer, Paul Von Ragué
Efficient diffuse function-augmented basis sets for anion
        calculations. III. The 3-21+G basis set for first-row
        elements, Li-F
J. Comput. Chem., 4, 294-301 (1983)
10.1002/jcc.540040303