Mishkat al-Masabih
Anas said that the Prophet (ﷺ) stood in humble supplication for a month and then gave it up. Abu Dawud and Nasa'i transmitted it.
وَعَنْ أَنَسٍ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَنَتَ شَهْرًا ثُمَّ تَرَكَهُ. رَوَاهُ أَبُو دَاوُد وَالنَّسَائِيّ
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