How did Muhammad encourage people to treat each other?

Answer 1

Prophet Muhammad (peace be upon him) called people of Mecca to prevent themselves from worshiping Idols as partners to Allah (God) and to worship the one and only one God (Allah) with no partner, no father, no son, no companion, and no resemblance and to believe in Muhammad as His prophet and messenger.

and after he was rejected from Mekkah and resided in Medinah he changed 180 degrees and the last teachings of his abrograte the misleading "softer" verses of Mekkah.

People of Mecca were idol worshippers. They wer plunged into the darknss of ignorance. They were drunkards, gamblers, cheaters and superstitious. They buried their daughters alive and had no respect for women. They exploited the poor and the weak. They followed no rule. Their motto was, "Might is right."

When the last Prophet of Islam Hazrat Muhammad (SAW) preached the message of Almighty Allah inviting the Meccans to worship only One Almighty Allah, to be honest, truthful, fair, and straightforward in their dealings, they turned against him. They were not ready to change their traditions, culture and the power over the poor and the slaves. They felt a threat.

Answer 2

Muhammad taught people to love each other and God. Muhammad taught people to don't hate each other and treat everybody equally.