Those who show no mercy will be shown no mercy

Abu Salmah (ra) related that Abu Hurayrah said,
“The prophet of Allah kissed Hassan Ibn ‘Ali while Aqra’ Ibn Habis was sitting nearby. Aqra’ said,
‘I have ten children and have never kissed anyone of them.’ The prophet looked at him and said,
‘Those who show no mercy will be shown no mercy.”

-Bukhari and Muslim-