1. Actions that are Allowed During the Prayer

2. Crying, moaning and Groaning
Whether due to a fear of Allah or to any other reason (e.g., a moan due to some pain or injury that one cannot contain), is permissible. This is based on the Qur'anic verse: "When the revelations of the Merciful were recited unto them, they fell prostrating and adoring." This verse is general and includes one who is praying.
Abdullah ibn ash-Schikhir relates: "I saw the Messenger of Allah praying and his chest was 'buzzing', like the buzzing of a cooking pot, due to crying." [This is related by Ahmad, Abu Dawud, an-Nasa'i, and at- Tirmizhi. ]
Ali reports: "There was no horseman among us at the battle of Badr save al-Miqdad ibn al-Aswad. I saw that not one of us was standing save the Messenger of Allah who was praying under a tree and crying until the dawn." This is related by Ibn Hibban.
Aishah relates the incident that occurred during the fatal illness of the Prophet. The Messenger of Allah said: "Order Abu Bakr to lead the people in prayer." 'Aishah responded: "O Messenger of Allah, Abu Bakr is a very soft-hearted man and he cannot control his tears, and if he recites the Qur'an, he cries." The Messenger of Allah said: "Order Abu Bakr to lead the people in salah. You women are like the companions of Yusuf." [This is related by Ahmad, Abu Dawud, Ibn Hibban, and at-Tirmizhi who calls it sahih]
The fact that the Prophet insisted that Abu Bakr lead the salah after he was inforrned that he would be overcome by weeping proves that it is permissible to cry while praying.
Umar prayed fajr and recited Surah Yusuf, and when he reached the verse "I expose my distress and anguish only unto Allah," he raised his voice in crying. [This is related by al-Bukhari]
In 'Umar's raising his voice in crying is a refutation of those who say that crying invalidates the salah if it causes a sound from the mouth, regardless of whether it is due to the fear of Allah or not. They argue that sound from the mouth due to crying is like speaking, but this is not acceptable as crying and speaking are two different things.

3. Turning due to some need
Ibn Abbas relates: "The Messenger of Allah would turn to his right and left he would not turn his head to see behind him." [This is related by Ahmad.]
Abu Dawud records that when the Prophet prayed, "he looked toward a valley because he had sent some horsemen to guard the valley."
Anas ibn Sireen says: "I saw Anas ibn Malik lift his eyes to something while he was praying."
[This is related by Ahmad.]

4. Movement during the Prayer is disliked and unnesasary movement can invalidate your prayer
Aishah says: "I asked the Messenger of Allah about turning in salah and he said: 'It is the portion that the Satan steals from the slave's prayer.'" [This is related by Ahmad, al- Bukhari, an-Nasa'i, and Abu Dawud.]
Abu ad-Darda' narrates from the Prophet: "O people, be careful about turning for there is no salah for the one who turns. If you must do it, do it in the voluntary prayers and not in the obligatory prayers." [This is related by Ahmad.]
Anas relates that the Messenger of Allah said to him: "Be careful about turning during the salah as turning in the salah is disastrous. If you must do it, then do it in the voluntary prayers but not in the obligatory prayers." [This is related by at-Tirmizhi who calls it sahih.]
Abu Zharr reported that the Prophet said: "Allah faces the slave while he is in the salah and keeps facing him as long as he does not turn. If [the slave] turns, [Allah] turns away from him." [This is related by Ahmad and by Abu Dawud]
The preceding hadith is concerned with turning the face during the salah. If one turns the whole (upper) body away from the qiblah, then the salah is invalidated, for not fulfilling the requirment of facing the qiblah.

5. Taking a few steps due to necessity is permissable if one remains facing Qibla and not too many steps
Aishah said: "The Messenger of Allah was offering salah in the house and the door was locked. I came and knocked on the door and he walked over to open it for me and then he returned to his place of prayer. The door was in the direction of the qiblah." [This is related by Ahmad, Abu Dawud, an-Nasa'i, and atTirmizhi].
It may be observed that in this hadith, he did not turn away from the qiblah either in opening the door, or in returning to his place. This is supported by what has been related that the Prophet would pray and if anyone knocked on the door, he would open the door provided the door was in the direction of the qiblah or on his right or on his left, but he would not turn his back to the qiblah.
Concerning taking a lot of steps, Ibn Hajr says in Fath al-Bari: "The jurists are agreed that taking many steps invalidates an obligatory prayer. But to take a few steps is okay

6. Holding a Child while Praying
Abdullah ibn Shidad relates that his father said: "The Messenger of Allah came to us either during the noon or afternoon prayers and he was carrying Hassan or Hussain. The Prophet proceeded to the front and put him down and made the takbir for the salah. During the salah, he made a long sajdah. I raised my head and saw the child on the back of the Messenger of Allah while he was in sajdah. I returned to my sajdah. When the Messenger of Allah finished the salah, the people said to him: 'O Messenger of Allah, you prostrated during your salah so long that we suspected you were thinking about some matter or you were receiving some revelation.' He said: 'None of that happened but my son was resting and I hated to rush him until he had finished what he desired."' [This is related by Ahmad, an-Nasa'i, and al-Hakim].
Abu Qatadah reports that the Prophet was offering salah and Umamah bint Zainab was on his neck [shoulder]. When he performed ruku', he put her down, and when he got up from his sajdah, he would place her back on his neck. '

7. Returning a Greeting by a motion
The one in salah who is greeted or spoken to may reply to the one who greets or speaks to him by making some motion.
Jabir said: "The Messenger of Allah sent me somewhere while he was going to the tribe of Mustaliq. I came to him and he was praying while on the back of his camel. [When] I spoke to him, he and Zubair motioned with their hands. I heard him reciting and saw him gesturing with his head. When he finished, he said: 'What have you done about the thing I sent you for? Nothing kept me from talking to you save that I was in salah.'" [This is related by Ahmad and Muslim.]
Abdullah ibn 'Umar narrates that Suhaib said: "I passed by the Messenger of Allah while he was offering salah. I greeted him and he responded to me by only signaling." [This is related by Ahmad and by at-Tirmizhi.]
Abdullah ibn 'Umar says: "I asked Suhaib: 'How did the Messenger of Allah respond to the people when they greeted him while he was praying?' He said: 'He would signal to them with his hand.'" [This is related by Ahmad, at- Tirmizhi, Abu Dawud, an-Nasa'i, and Ibn Majah.]
The same applies to signaling with one's finger or hand or by nodding the head. All of these actions have been related from the Prophet

8. If a mistake is made in prayer:
It is allowed for men to say subhanallah and for women to clap if there is some need to do so (such as alerting the imam to a mistake or informing someone that he or she may enter the room or to warn a blind person, and so on).
Sahl ibn Sa'd asSa'di relates that the Prophet said: "If someone is faced with something during the salah, he should say 'subhanallah.' Clapping is for the women and saying subhanallah is for the men."
[This is related by Ahmad, Abu Dawud, and an-Nasa'i.]

9. Responding to one who sneezes while praying
Rifa'ah ibn Rafi' relates: "I prayed behind the Messenger of Allah, and I sneezed and said, 'Praise be to Allah, a great deal of praise, beautiful and blessed, as our Lord loves and is pleased with.' [Afterward,] the Messenger of Allah asked: 'Who spoke during the salah?' No one said anything. He asked again, and no one said anything. He asked again, and I said: 'It was I, O Messenger of Allah!' He then said: 'By the One in whose hand is Muhammad's soul, thirty some odd angels raced to get that phrase to raise it [to the Lord].'"
[This is related by an-Nasa'i and at- Tirmizhi, and by al-Bukhari with a different wording.]

10. Questions?