  We report $^{75}$As NMR studies on single crystals of rare-earth doped iron
pnictides superconductor Ca$_{1-x}$Pr$_{x}$Fe$_{2}$As$_{2}$ ($x$=0.075 and
0.15). The $^{75}$As spectra show a chemical pressure effect with doping and a
first order structure transition to the collapsed tetragonal phase upon
cooling. A sharp drop of the Knight shift is seen below the structural
transition, whereas $1/T_1$ is strongly enhanced at low-temperatures. These
evidences indicate quenching of Fe local magnetism and short-range ordering of
Pr$^{3+}$ moment in the collapsed tetragonal phase. The quenched Fe moment
through structure collapse suggests a strong interplay of structure and
magnetism, which is important for understanding the nature of the collapsed
tetragonal phase.
