Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) say: Whoever does not catch the bowing (ruku') is not to count the prostration.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2402