All praise be to Allaah. May peace and blessings be upon the Messenger of Allaah, his family, and Companions. Many people from here and abroad inquire about the position of placing the hands after Rukoo` (bowing). Thus, I opine to give a detailed answer for this out of sincere advice for Muslims, to display the truth, clarify ambiguity, and propagate the Sunnah (whatever is reported from the Prophet). In explanation, I can say that it was authentically established in the Sunnah of the Messenger of Allaah (peace be upon him) that he used to place his right hand on his left forearm when he was standing in Salaah (Prayer) and that he (peace be upon him) used to command Muslims to do so.
It was stated by Imaam Al-Bukhaaree (may Allaah be merciful to him) in his Saheeh Book of Hadeeth (in the chapter entitled placing the right hand upon the left one) that `Abdullaah ibn Maslamah reported from Maalik, from Aboo Hazim that Sahl ibn Sa`d (may Allaah be pleased with him) said: The people were ordered to place the right hand on the left forearm in Salaah (Prayer). Aboo Hazim remarked: “I do not know except that he attributed it (i.e., the report) to the Prophet (peace be upon him).”
We can infer from this authentic Hadeeth that it an act of Sunnah to place the right hand upon the left one while standing in Salaah both before and after Rukoo` (bowing) through the fact that Sahl said that people were ordered to place the right hand on the left forearm in Salaah. It is known that it is an act of Sunnah for the one who is performing Salaah to place the palms on the knees when in a state of Rukoo`, and to place them on the floor by his shoulders or his ears when in the state of Sujood (prostration), and to place them on both his thighs and knees while in both the states of sitting between the two prostrations and reciting Tashah-hud (a recitation in the sitting position in the second/last unit of Prayer) according to what is explained in the Sunnah of the Prophet in this regard. Thus, it is only the position of standing that is not mentioned. Accordingly, it is concluded from the report of Sahl that it is such position that is meant. Thus, it should be clear that it is an act of Sunnah for the one who is performing Salaah to place his right hand over his left forearm while in the state of standing up in his Salaah, whether standing both before or after performing Rukoo`, because it was not reported from the Prophet (peace be upon him) that he differentiated between them as far as we know. As for a person who differentiates between them, he has to bring evidence for this… read more here.