A freed slave (mawla) of Quraysh who was called Ibn Marsa said: I was sitting with Umar bin al-Khattab (may Allah be pleased with him). When he had led the Zuhr prayer, he said: O Yarfa! Bring the letter, meaning a letter which Umar had written concerning the paternal aunt, asking about her and seeking Allah's guidance (istikharah) about her. When Yarfa brought that letter, Sayyiduna Umar (may Allah be pleased with him) called for a metal vessel or a cup with water in it, and he erased that letter in it. Then he said: If Allah had been pleased with you, He would have kept you; if Allah had been pleased with you, He would have kept you.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12206