If I arrive late and the imam is already prostrating, should I join immediately with the takbir and prostrate, or wait until the imam stands for the next rak'ah?

Summary

A latecomer is encouraged to join the congregational prayer at once in whatever position the imam is in, whether standing, bowing, prostrating or sitting, rather than waiting for the imam to rise for the next rak'ah. The fatwa relies on hadiths instructing followers to do as the imam does, along with the views of scholars such as al-Shawkani and Ibn Hajar. However, the rak'ah is not counted if one joins after the imam has risen from bowing, or during prostration, sitting between prostrations or the final sitting. A rak'ah is gained only if one surely catches the bowing with the imam before he rises.

Written in our own words from the original fatwa — check the source before acting on it.