Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.092B.
Section : Motioning with both hands while making the salutations [i.e., the taslim].
Jabir ibn Samurah said: “We prayed behind the Prophet and he said: ‘What is wrong with them that they make salutation with their hands as if they were the tails of horses? It is enough for you to place your hand on your thigh and say, as salam ‘alaikum, as salam ‘alaikum!'” This is related by an-Nasa’i and others.