Hadith 2181

This hadith of Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) is also about the same issue that I saw the Noble Prophet (peace be upon him) on the morning of the twenty-first night, and there was mud on his forehead and the tip of his nose. Because the Prophet (peace be upon him) had told the noble companions that he had seen himself prostrating in mud during Laylat al-Qadr, so the twenty-first night, according to the days that had passed in the month, was an odd night. It is possible that in that year, Ramadan was of twenty-nine days. In this way, that night, according to the remaining days, was the ninth night, while according to the days that had passed, it was the twenty-first night.
Hadith Reference صحيح ابن خزيمه / 2181
Hadith Takhrij صحيح مسلم