Sayyiduna Ammar bin Yasir (may Allah be pleased with him) said: On one of the journeys of the Prophet (peace and blessings be upon him), a necklace of Sayyidah Aishah (may Allah be pleased with her) made of Zafar onyx beads was lost, and Sayyidah Aishah (may Allah be pleased with her) was with the Messenger of Allah (peace and blessings be upon him) on that journey. Sayyidah Aishah (may Allah be pleased with her) searched for her necklace until the night came to an end. Sayyiduna Abu Bakr (may Allah be pleased with him) came and was angry with her, and said: You have held the people back in a place where there is no water. The narrator said: Then the verse of al-Sa'id (tayammum) was revealed. Sayyiduna Abu Bakr (may Allah be pleased with him) came and said: By Allah, O my daughter! As far as I know, you are truly blessed. Ubaydullah said that Ammar used to narrate: On that day the people struck the ground with their palms and wiped their faces, then struck again and wiped their hands up to the shoulders and armpits, then they prayed.
(b) In another narration Ma'mar and Yunus also mention two strikes, just as Ibn Abi Dhi'b mentioned two strikes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1001