Mishkat al-Masabih 29 Excellent Qualities and Description of the Prophet كتاب الفضائل والشمائل 27

وَعَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «سلوا الله الْوَسِيلَةَ» قَالُوا: يَا رَسُولَ اللَّهِ وَمَا الْوَسِيلَةُ؟ قَالَ: «أَعْلَى دَرَجَةٍ فِي الْجَنَّةِ لَا يَنَالُهَا إِلَّا رجلٌ واحدٌ وَأَرْجُو أَنْ أَكُونَ أَنَا هُوَ» . رَوَاهُ التِّرْمِذِيُّ

He reported the Prophet as saying, “Ask God to grant me the wasila .” God’s messenger was asked what the wasila meant and replied, “The highest grade in paradise which only one man will attain, and I hope I may be he.” Tirmidhi transmitted it.