What is the punishment for abandoning a sin and then returning to it?

If a person returns to a sin from which he had repented, he exposes himself to punishment, and his first repentance is accepted if it fulfilled its conditions. The servant should not despair but should repeat repentance while fulfilling its conditions: the resolve not to return [to the sin], abandoning it, and regretting it. Allah accepts repentance no matter how often the sin is repeated. To avoid returning to sin, one should be mindful of Allah and remember His constant watch, continuously remember Him and supplicate to Him to keep the heart firm, keep company with the righteous, and read the biographies of our righteous predecessors.