What is to be avoided in prayer and what is not

It is narrated from Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) that he asked the Messenger of Allah (peace and blessings be upon him) about praying with a bow slung on, and he (peace and blessings be upon him) said: "Pray wearing the bow, but take off the quiver."
Ishaq (may Allah have mercy on him) said that Isa bin Yunus also narrated this hadith to us through Uqbah bin Khalid, and Isa explained it, saying that "al-qaran" means the small quiver or arrow bag that hunters carry.
Ishaq also said that Abdullah bin Nafi' al-Sa'igh narrated the like of it to us through Musa with the same chain.
And Imam Abu Ya'la said: Abu Bakr narrated this same hadith to us.

It is narrated from Sayyiduna Wathilah (may Allah be pleased with him) that he said: "When we were with the Messenger of Allah (peace and blessings be upon him) in the military camp and the iqamah was called for the prayer, we would rush at once to our bows and swords (and take them up), and then pray in them in the place of a cloak (slinging them on the body or holding them), so that they served us in place of a cloak."
Imam Ahmad bin Mani' narrated this hadith in his Musnad; this narration makes clear the juristic legitimacy of praying with weapons in a state of war or for the needs of defence.

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that he said: "The Messenger of Allah (peace and blessings be upon him) forbade me to pray while my hair was braided into a knot (at the back of the head), and (forbade me) to turn over the pebbles (of the place of prostration) during the prayer."
Imam Musaddad recorded this narration in his Musnad through Abd al-Warith, Muhammad bin Ishaq, Abu Ishaq and al-Harith.

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever buys a garment for ten dirhams, and one dirham of them is unlawful, Allah Almighty will not accept any prayer of his as long as that garment is on his body." Then Sayyiduna Ibn Umar (may Allah be pleased with them both) put his two fingers into his ears and said: "May these two ears of mine become deaf if I did not hear the Prophet (peace and blessings be upon him) saying it myself."
Imam Abd bin Humayd narrated this hadith in his Musnad (813). Because of the tadlis (concealment in the chain) of Baqiyyah bin al-Walid and the obscurity of Uthman bin Zufar in its chain, some scholars of hadith declared it da'if (weak); however, corroborating chains and supporting witnesses for it are also found in Musnad Ahmad and elsewhere.

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) took off his sandals during the prayer, and the followers behind him also took off their shoes (in following him). He (peace and blessings be upon him) asked (after the prayer): "What made you take off your shoes?" They said: O Messenger of Allah! We saw you taking off your shoes, so we took off ours too. He (peace and blessings be upon him) said: "In fact, Jibril (peace be upon him) came and informed me that there was filth on one of them (the shoes), and for that reason I took them off; so do not take off your shoes (without a reason)."
The narrator named Abu Hamzah is da'if (weak).

It is narrated from Bakr bin Abdullah al-Muzani (may Allah have mercy on him) that the Prophet (peace and blessings be upon him) offered the prayer and took off his shoes (during the prayer), and the people also took off their shoes (in following him). He (peace and blessings be upon him) asked them: "Why did you take off your shoes?" They said: You took off your shoes, so we took ours off too. He (peace and blessings be upon him) said: "In fact, Jibril (peace be upon him) came and informed me that there was some filth on these shoes. So when one of you comes to the mosque, let him turn his shoes over and look (at their soles); if he finds any filth or impurity on them, let him take them off; otherwise let him pray in them (wearing them)."
This narration is mursal (the Successor omits the Companion).

It is narrated from a Bedouin (desert Arab) who saw the Prophet (peace and blessings be upon him) that he said: "I saw the Prophet (peace and blessings be upon him) praying while he (peace and blessings be upon him) was wearing shoes made of camel leather. Then (during the prayer) he (peace and blessings be upon him) spat to his left and then rubbed with his shoe the spot where he (peace and blessings be upon him) had spat."
Imam Ahmad recorded this narration in the Musnad. Its chain contains an unnamed narrator (whose name is not mentioned), because of which it is weak in terms of its chain; however, the subject of praying in shoes, and, when needed, spitting to the left and wiping it away by rubbing it with the shoe, is found in other sahih hadith.

It is narrated from Alqamah bin Qays (although the narrator's hearing from Alqamah is not established) that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) came to the house of Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him), and the time of prayer arrived. Sayyiduna Abu Musa (may Allah be pleased with him) said (out of respect for him): "O Abu Abd al-Rahman! Step forward to lead the prayer, for you are older than me in age and superior to me in knowledge as well." Sayyiduna Abdullah (may Allah be pleased with him) said: "No, rather you step forward, for we have come to you in your house and your mosque (place of prayer), so you are more entitled to lead." So Sayyiduna Abu Musa (may Allah be pleased with him) stepped forward and took off his shoes (for the prayer). When he finished with the salam, Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) asked him (by way of question): "What did you intend by taking them off? Are you in the sacred valley of Tuwa [Surah Ta Ha: 12]?"
This narration is munqati' (broken), because Abu Ishaq's hearing from Alqamah bin Qays is not established.

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that "the Messenger of Allah (peace and blessings be upon him) used to pray in his leather socks (khuffs)."
Imam Abu Ya'la narrated it in his Musnad; its chain contains a narrator named Umar bin Nabhan, who is da'if (weak); however, praying in leather socks is established and transmitted in other sahih and authoritative hadith.

It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that "the Messenger of Allah (peace and blessings be upon him) forbade a man to pray while the hair of his head is tied up or knotted into a bun (at the back)."
(Imam Ishaq said:) I asked al-Mu'ammal whether Sayyidah Umm Salamah (may Allah be pleased with her) is mentioned in the chain of this narration. He replied: I have no doubt at all about it; I first wrote it down from him in this way in Makkah. I (Ibn Hajar) say: Abd al-Razzaq and Waki' also narrated this hadith from Sufyan al-Thawri, but in their narration Sayyidah Umm Salamah (may Allah be pleased with her) is not mentioned; Imam Ahmad (may Allah have mercy on him) recorded it in his book through these two teachers, and it was because of this discrepancy that Ishaq sought confirmation of it again from al-Mu'ammal. So if al-Mu'ammal preserved it correctly, then this discrepancy lies within Sufyan's own narration (in that he sometimes narrated it from Umm Salamah and sometimes without her), and is not an objection against him. And Allah knows best.