Musannaf Ibn Abi Shaybah

Hazrat Harith bin Qais, may Allah have mercy on him, said: When you are engaged in a worldly task, complete it quickly, and if you are engaged in a task of the Hereafter, do it calmly and with as much composure as possible. And when Satan comes to you during prayer and says that you are showing off, then perform the prayer more and make it longer.