Hadith 6:684
Abu Usama narrated to us, from Hisham, from Muhammad, who said: "He performs the Takbir for what he catches, and he makes up what he missed." And Al-Hasan said: "He performs the Takbir for what he catches, and he does not make up what he missed."
حدثنا أبو أسامة عن هشام عن محمد قال يكبر ما أدرك ويقضي ما سبقه وقال الحسن يكبر ما أدرك ولا يقضي ما سبقه