I heard the Messenger of Allah ﷺ say, "Whoever is deprived of gentleness is deprived of all goodness."
سمعت رسول الله ﷺ يقول: من يحرم الرفق يحرم الخير.
No references are available.
Muslim narrated it in The Book of Righteousness and Kinship Ties (2592:74–75) through several routes from Tamim bin Salama, from Abdul-Rahman bin Hilal Absi, from Jareer, who mentioned it.