Sahih Muslim Book 6, Hadith 67
Ibn 'Abbas one day addressed us in the afternoon (after the afternoon prayer) till the sun disappeared and the stars appeared, and the people began to say: Prayer, prayer. A person from Banu Tamim came there. He neither slackened nor turned away, but (continued crying): Prayer, prayer. Ibn 'Abbas said: May you be deprived of your mother, do you teach me Sunnah? And then he said: I saw the Messenger of Allah (ﷺ) combining the noon and afternoon prayers and the sunset and 'Isha' prayers. 'Abdullah b. Shaqiq said: Some doubt was created in my mind about it. So I came to Abu Huraira and asked him (about it) and he testified his assertion.
Ibn 'Abbas reported that the Messenger of Allah (ﷺ) observed in Medina seven (rak'ahs) and eight (rak'ahs), i. e. (be combined) the noon and afternoon prayers (eight rak'ahs) and the sunset and 'Isha' prayers (seven rak'ahs).
A person said to Ibn 'Abbas (as he delayed the prayer): Prayer. He kept silence. He again said: Prayer. He again kept silence, and he again cried: Prayer. He again kept silence and said: May you be deprived of your mother, do you teach us about prayer? We used to combine two prayers during the life of the Messenger of Allah (ﷺ).