Riyad as-Salihin: The Book of Virtues – Hadith No. 509 — Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah… (Hadith No. 509)

Abu Hurairah (May Allah be pleased with him) reported: 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.".

Explanation:

Reference: Riyad as-Salihin, The Book of Virtues, Hadith No. 509