Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "When you come to the prayer, come to it with dignity and tranquillity. Pray whatever of it you catch, and make up (that is, perform afterwards) whatever you have missed."
Tabarani recorded it in al-Mu'jam al-Awsat as a narration of Abu al-Sari from Sayyiduna Sa'd (may Allah be pleased with him). I have not found anyone who mentions him (that is, Abu al-Sari), and the rest of its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2089
Hadith Gradingمحدثین:إسنادہ ضعیف
Hadith Takhrij«أخرجه المعجم الأوسط للطبراني برقم: 1357»