From Sahih Muslim (Hadith 1629):
Ibn 'Abbas reported:The Messenger of Allah (ﷺ) observed the noon and afternoon prayers together in Medina without being in a state of fear or in a state of journey. (Abu Zubair said: I asked Sa'id [one of the narrators] why he did that. He said: I asked Ibn 'Abbas as you have asked me, and he replied that he [the Holy Prophet] wanted that no one among his Ummah should be put to [unnecessary] hardship
Reference: Muslim 1629