All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The mention of Allaah and supplications after completing the obligatory prayers should be recited straight after finishing the obligatory prayers and they should not be delayed until after finishing the supererogatory prayers. We have discussed this issue in Fataawa 83197 and 89938.
According to the view of the majority of the scholars supplicating after the obligatory prayer and finishing the Tasbeeh is desirable and not obligatory, because when the Prophet was asked which supplication is more likely to be answered, he said: “The last part of the night and after the obligatory prayers….” [At-Tirmithi]
We have already issued Fataawa 84069 and 85058 clarifying the ruling of supplicating after the obligatory prayers. However, restricting the supplication to one obligatory prayer only is not from the Sunnah.
As regards your question whether or not the supplication will be answered, then you should know that Allaah promised to answer the supplication of whoever fulfils the conditions of the acceptance of the supplication. The answer to a supplication is either by giving the supplicator what he precisely asked for, or repelling harm from him, or saving the reward of his supplication for the Day of Judgment. However, the acceptance of a particular supplication is a matter that depends on Allaah and no one knows whether the supplication will be accepted or rejected because this is a matter of the unseen.
Moreover, it is permissible for a person to supplicate his Lord when sleeping and when walking. It is confirmed that when the Prophet wanted to sleep, he would put his right hand under his cheek and then he would say: “O Allaah, protect me from Your Punishment on the Day You resurrect your Servants.” [Abu Daawood and At-Tirmithi]
It is also confirmed that the Prophet supplicated when performing Tawaaf, when going out of his house, and this is evidence that it is permissible to supplicate when walking.
On the other hand, raising the hands when supplicating is desirable in general and it is a Sunnah to do so, and it is one of the reasons for the supplication in being answered. Therefore, it is possible for the supplicator to raise his hands whether he supplicated when walking, or lying on a bed or else. However, one should not raise his hands in circumstances when the Prophet supplicated but did not raise his hands, like the supplication when going to sleep “O Allaah, protect me from Your Punishment on the Day You resurrect your Servants.”, as he put his noble hands under his cheek, and when he supplicated in Friday Khutbah, and so forth.
For more benefit on raising hands when supplicating, please refer to Fatwa 84676 and 87633.
Allaah Knows best.