Adab 3–6: Cough, Yawn, Standing for Iqamah, and the Imam's Start

The Sunnahs of Prayer, Part 3: Final Sitting, Salaam, and Adab

وَدَفْعُ السُّعَالِ مَا اسْتَطَاعَ، وَكَظْمُ فَمِهِ عِنْدَ التَّثَاؤُبِ، وَالْقِيَامُ حِينَ قِيلَ حَيَّ عَلَى الْفَلَاحِ، وَشُرُوعُ الْإِمَامِ مُذْ قِيلَ قَدْ قَامَتِ الصَّلَاةُ

3. Suppress unnecessary coughing as far as reasonably possible.
4. Restrain/cover the mouth when yawning.
5. The text lists standing when حَيَّ عَلَى الْفَلَاحِ is called during Iqamah.
6. It permits the Imam to begin from قَدْ قَامَتِ الصَّلَاةُ; the commentary notes that delaying until the Iqamah is completed is better.

These are Adab, not conditions that determine whether the prayer is valid.