Ikrimah bin Khalid (may Allah have mercy on him) narrated that Sa'id bin Jubayr (may Allah have mercy on him) informed him that he heard Sayyiduna Ibn Abbas (may Allah be pleased with them both) say: I saw Umar (may Allah be pleased with him) recite Surah Sad [Surah Sad: 1] on the pulpit; when he reached the verse of prostration, he came down from the pulpit and prostrated, then went back up onto the pulpit.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3744