What is the difference between "isbir" (be patient) and "istabir" (persevere in patience)?

There is no difference in meaning between "isbir" (اصبر) and "istabir" (اصطبر), as both are commands to be patient. However, "istabir" (اصطبر) is more emphatic in meaning and has a greater number of letters in its structure. Its origin is "istabar" (اصتبر) with a ta (ت), but its ta was replaced with a ṭa (ط) to harmonize with the ṣad (ص), as both are letters of isti'la (elevation), iṭbaq (closure), and tafkhim (emphasis). The Arabs increase the meaning when they increase the letters in the word's structure, and the increase here signifies emphasis.