历久弥坚
lì jiǔ mí jiān
Meaning: to become more resolute with the passing of time
Original: "习近平强调,中朝传统友谊历久弥坚,是双方共同的宝贵财富。"
Translation: "Xi Jinping stressed that the traditional and increasingly strong friendship between China and the DPRK is the common treasure of both parties" (Ministry of Foreign Affairs, PRC)
Source: On September 9, Xi Jinping sent a congratulatory message to Kim Jong Un on the 73rd anniversary of North Korea's National Day