From Sahih Muslim (Hadith 1448):
Thabit reported:They (the believers) asked Anas about the ring of the Messenger of Allah (ﷺ) and he said: One night the Messenger of Allah (ﷺ) delayed (observing) the 'Isya' prayer up to the midnight or midnight was about to be over. He then came and said: (Other) people have offered prayers and slept, but you are constantly in prayer as long as you wait for prayer. Anas said: I perceive as if I am seeing the lustre of his silver ring, and lifted his, small left finger (in order to show how the Prophet had lifted it)
Reference: Muslim 1448