Abu al-Ahwas relates: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: When you are behind the imam, do not bow until he has bowed, do not prostrate until he has prostrated, and do not raise your head before him. When the imam has finished (the prayer) and has neither stood up nor turned from his place, and you have some need, then go and leave him, for your prayer is complete.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2419
Hadith Gradingمحدثین:إسنادہ صحیح، اس کے راوی ثقہ ہیں۔