Musannaf Ibn Abi Shaybah 3894 — When a traveller joins the prayer

Ibn Awn said: I came to Madinah and caught one rak'ah of the Isha prayer. I began thinking to myself: What should I do now? Later I asked al-Qasim about it, and he said: Were you afraid that if you prayed four rak'ahs Allah Almighty would punish you?!