Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.043A.

It is preferred to supplicate for the deceased after the fourth takbir, even though the supplicant rnay have done so after the third takbir. This is based on a narration by Ahmad on the authority of ‘Abdullah ibn Abi Awfa who said that when his daughter died, at his funeral prayer for her he made four takbirs. After the fourth takbir, he stood supplicating for as much as he did in between the other takbirs. Then he said: “The Prophet, peace be upon him, used to do the same in a funeral prayer.”

Ash-Shafi’i said: “After the fourth takbir one may say, Allahumma la tuharimna ajrahu wa la taftinna ba’dahu. ‘O Allah! Do not deprive us of reward for (supplicating for) him/her, nor put us to trial after him (or her)’.”

Ibn Abu Hurairah said: “After the fourth takbir the elders used to say: Allahumma Rabbana atina fi ad-Dunya hasanatan wafi al-Akhirati hasanatan wa qina ‘azhab an-Nar. ‘O Allah! Grant us good in this life and good in the life to come, and save us from the torment of Hell Fire.”