Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: No recitation or specific supplication has been fixed for us in the funeral prayer. When the imam says the takbir, you too say the takbir, and say good words in abundance (that is, supplicate for the deceased with good words).
Ahmad recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 4153