When did islam come to china?

The History of Islam in China began when four Sahabas- Sa'ad ibn abi Waqqas (b.594-d.674 AD), Wahb Abu Kabcha, Jafar ibn Abu Talib and Jahsh (a father-in-law of Prophet Muhammad)preached in 616/17 and onwards in China after coming from Chittagong-Kamrup-Manipur route after sailing from Abyssinia in 615/16. Sa'ad ibn abi Waqqas later, after conquest of Persia in 636, went with Sa'id ibn Zaid (b.594- d.673 AD), Qais ibn Sa'd (d.682 AD) and Hassan ibn Thabit to China in 637 taking the complete volume of the Quran. Sa'ad ibn abi Waqqas again headed for China for the third time in 650-51 after Caliph Uthman asked him to lead an embassy to China, which the Chinese emperor received warmly.