Uposathasutta

ud5.5:8.1 Then the Buddha said to the monks,

ud5.5:8.2 “From this day forth, monks, I will not perform the sabbath or recite the monastic code.

ud5.5:8.3 Now you should perform the sabbath and recite the monastic code.

ud5.5:8.4 It’s impossible, monks, it can’t happen that a Realized One could recite the monastic code in an impure assembly.