Hadith 7:29
Sahl b. Sa‘d told of the Prophet being accustomed to place his two fingers opposite his shoulders and make supplication.
وَعَن سهل بن سَعْدٍ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: كَانَ يَجْعَل أصبعيه حذاء مَنْكِبَيْه وَيَدْعُو
Original Reference: Mishkat al-Masabih 2254