Genesis 38:5

And she yet again conceived, and bare a son; and called his name Shelah; and he was at Chezib, when she bare him. The older sons may thus have been born at Adullam, a city of some importance in later times, Joshua 12:15; Joshua 15:35; 2 Chronicles 11:7; Micah 1:15. Chezib, where Judah was tenting at the time of Shelah's birth, Joshua 15:44; Micah 1:14, was in the southern part of what was afterward the Plain of Judah. Apparently there was not much difference in the age of the three sons, for the entire story, as here related, took place between the incident at Dothan and the removal of Jacob to Egypt, a period of about twenty-three years.