The 877 series do not have an internal oscillators.
You must provide a signal by means of a crystal, ceramic resonator, R/C or some other form of signal generator, depending on the accuracy you need, though crystals are accurate and cheap enough.
For an internal oscillator you will have to choose another 16F chip with that feature, use Microchips Parameter search to find suitable ones. though most are limited to a max frequency of 4 or 8 Mhz PIC16 MCU - Product Family - 8-bit Microcontrollers