Listed as a chengyu in 《
新华成语词典》 (Xinhua Chengyu Dictionary), with derivation cited from Lao She's 《
骆驼祥子》 (Camel Xiangzi / Rickshaw Boy, 1936), Chapter 13:
结结巴巴的,
他把昨夜晚的事说了一遍 — 'haltingly, he told over what had happened the night before'. The phrase is built by reduplicating
结巴 'stutter' (jiēba) with the AABB pattern that intensifies adjectives in Chinese.