Slipping motions of magnetic field lines are a distinct signature of three-dimensional magnetic reconnection, a fundamental process driving solar and stellar flares. While being a key prediction of numerical experiments, the rapid super-Alfvénic field line slippage driven by the ‘slip-running’ reconnection has remained elusive in previous observations. New frontiers into exploring transient flare phenomena were introduced by recently designed high cadence observing programs of the Interface Region Imaging Spectrograph (IRIS). By exploiting high temporal resolution imagery (~2 s) of IRIS, here we reveal slipping motions of flare kernels at speeds reaching thousands of kilometres per second. The fast kernel motions are direct evidence of slip-running reconnection in quasi-separatrix layers, regions where magnetic field strongly changes its connectivity. Our results provide observational proof of theoretical predictions unaddressed for nearly two decades and extend the range of magnetic field configurations where reconnection-related phenomena can occur.

磁力线的滑动运动是三维磁重联的一个独特特征，这是驱动太阳和恒星耀斑的基本过程。虽然是数值实验的关键预测，但由“滑移运行”重新连接驱动的快速超 Alfvénic 场线滑移在以前的观测中仍然难以捉摸。最近设计的界面区域成像光谱仪 （IRIS） 的高节奏观测程序为探索瞬态耀斑现象引入了新的前沿。通过利用 IRIS 的高时间分辨率图像 （~2 s），我们揭示了耀斑核以每秒数千公里的速度滑动运动。快速的内核运动是准分离层中滑运行重新连接的直接证据，这些区域是磁场强烈改变其连接性的区域。我们的结果为近二十年来未得到解决的理论预测提供了观测证据，并扩展了可能发生重新连接相关现象的磁场配置范围。