Riyad us Saliheen: Hadith 1187

The Messenger of Allah (ﷺ) used to urge (the people) to perform (optional Tarawih) prayer at night during the month of Ramadan. He did not order them or make it obligatory on them. He (ﷺ) said, "Whosoever performs (optional Tarawih) prayers at night during the month of Ramadan, with Faith and in the hope of receiving Allah's reward, will have his past sins forgiven."

[Muslim].