From Sahih Muslim (Hadith 1635):
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)
Reference: Muslim 1635