同生死，共患难tóng shēng sǐ , gòng huàn nàn

cast(/throw) in one’s lot with sb;come together through thick and thin; for better (or) for worse;go through hardships and tribulations together; share weal and woe with; take the rough and the smooth together
❍ 张嘉庆心里说： “还是老同志呀！～ ……” (梁斌《红旗谱》370) Jiaqing was thinking: “He’s a trusty comrade,all right. A good man to have by you in a pinch and to share your troubles with…”

同生死，共患难tong sheng si,gong huan nan

go through fire and water together