(a) Amir bin Abdullah bin al-Zubayr narrates from his father (may Allah be pleased with him) that he said: "When the Prophet (peace and blessings be upon him) supplicated in the tashahhud, he would point with his finger and would not move it."
(b) Amir narrates from his father (may Allah be pleased with him) that he saw the Prophet (peace and blessings be upon him) supplicating in the same way: "He (peace and blessings be upon him) had placed his left hand on his left thigh."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2786
Wa'il bin Hujr (may Allah be pleased with him) said: I thought to myself that I would certainly watch the prayer of the Messenger of Allah (peace and blessings be upon him), how he (peace and blessings be upon him) prays. He mentioned the complete hadith. In it is: He (peace and blessings be upon him) sat with his left foot laid flat, placed his palm on his left thigh and knee, and placed his right elbow on his right thigh. Then he closed three of his fingers and formed a ring, then raised the index finger; he (peace and blessings be upon him) kept moving it, supplicating with it.
(b) It is possible that what is meant by moving it is pointing with the finger, not moving it continuously. In this way this hadith would agree with the narration of Ibn al-Zubayr (may Allah be pleased with them both). And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2787
It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Moving the finger in the prayer is like a spear against Satan."
(b) Mujahid (may Allah have mercy on him) said: A man's moving his finger in the tashahhud of the prayer is a hammer against Satan.
Muhammad bin Umar al-Waqidi alone narrated the hadith of Ibn Umar, and he is not strong.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2788