Sayyiduna Abdullah bin Zubair (may Allah be pleased with them both) said: I saw the Noble Prophet (peace and blessings be upon him) making supplication (gesture) in this way during prayer (at the time of Tashahhud). Ibn Uyaynah gestured with his finger, and Abu al-Walid (narrated that) he gestured with the index finger.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1375
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده حسن من أجل ابن عجلان، [مكتبه الشامله نمبر: 1377]
It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that when the Noble Prophet (peace and blessings be upon him) would sit at the end of the prayer (for Tashahhud), he would place his left hand on his left knee and his right hand on his right knee, and he would keep his finger raised.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1376