Al-Sha'bi narrates that Zayd bin Thabit (may Allah be pleased with him) said four takbirs in the funeral prayer for his mother, and I did not consider it to be any fixed limit. Then a mount was brought for him, and Ibn Abbas (may Allah be pleased with them both) held his stirrup. Zayd said to him: "Leave it, let it be." Ibn Abbas said: "This is how we treat the senior scholars."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4729