Abu Huraira told how when a man was making supplication using two of his fingers, God’s Messenger said, “Use one, use one.” It is transmitted by Tirmidhi and Nasa’i and by Baihaqi in <i>[Kitab] ad-da'awat al kabir</i>.

وَعَن أبي هُرَيْرَة قَالَ: إِنَّ رَجُلًا كَانَ يَدْعُو بِأُصْبُعَيْهِ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أَحِّدْ أَحِّدْ» . رَوَاهُ التِّرْمِذِيُّ وَالنَّسَائِيُّ وَالْبَيْهَقِيُّ فِي الدَّعَوَاتِ الْكَبِير