Mishkat al-Masabih 4 Prayer كتاب الصلاة 335

وَعَن عبد الله بن الزبير قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُشِيرُ بِأُصْبُعِهِ إِذَا دَعَا وَلَا يُحَرِّكُهَا. رَوَاهُ أَبُو دَاوُدَ وَالنَّسَائِيّ وَزَاد أَبُو دَاوُد وَلَا يُجَاوز بَصَره إِشَارَته

‘Abdallah b. az-Zubair said that the Prophet used to point with his [fore] finger when he made supplication, but did not move it. Abu Dawud and Nasa’i transmitted it, Abu Dawud adding that he kept his look fixed on the finger he was pointing.