Abû Hurayrah relates that Allah’s Messenger (peace be upon him) said: “Islam began strange, and it will become strange again just like it was at the beginning, so blessed are the strangers.” [Sahîh Muslim (1/130)]

`Amr b. `Awf relates that Allah’s Messenger (peace be upon him) said: “The religion will shrink back to the Hijâz like the snake shrinks back into its hole. It will cling to the Hijâz like the mountain goat clings to the mountaintop. The religion began strange, and it will become strange again just like it was at the beginning, so blessed are the strangers who restore what the people corrupt of my Sunnah.” [Sunan al-Tirmidhî (#2630)] Al-Tirmidhî grades it as good and authentic (hasan sahîh).

`Abd Allah b. `Amr b. al-`As relates that Allah’s Messenger (peace be upon him), said one day when the Companions were with him: “Blessed are the strangers.” He was then asked: “Who are the strangers, O Messenger of Allah?” He replied: “They are righteous people among many evil people who disobey them. more than they obey them.” [Musnad Ahmad (2/177 & 2/222) and Ibn al-Mubârak, Kitâb al-Zuhd (#775 p. 267)]
Some acts are attached to islam but became strange due to abandonment of them . In the case of put on shoe to observe SALAH is permissible even is the ASLU(basic). The following hadeeth are the evvidences for it:- The Prophet (peace and blessings of Allaah be upon him) entered the mosque in shoes and prayed in shoes. Abu Dawood narrated in his Sunan with his isnaad that Abu Sa’eed al-Khudri said: Whilst the Prophet (peace and blessings of Allaah be upon him) was leading his companions in prayer, he took off his shoes and placed them to his left. When the people saw that, they took off their shoes. When the Messenger of Allaah had finished the prayer he said, “What made you take off your shoes?” They said, “We saw you take off your shoes, so we took off our shoes.” The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Jibreel (peace be upon him) came to me and told me that there was some dirt on them.” And he said: “When one of you comes to the mosque, let him check his shoes, and if he seeds any dirt on them, let him wipe them and pray in them.” 

Abu Dawood also narrated from Ya’la ibn Shaddaad ibn Aws that his father said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Be different from the Jews, for they do not pray in their shoes or their khufoof (leather slippers).” 

And Abu Dawood narrated from ‘Amr ibn Shu’ayb, from his father, that his grandfather said: I saw the Messenger of Allaah (peace and blessings of Allaah be upon him) praying both barefoot and wearing shoes. This was also narrated by Ibn Maajah.   

But now that mosques are usually furnished with fine carpets, the one who enters the mosque should take off his shoes and be careful to keep the carpet clean and not annoy other worshippers because of dirt that may get onto the carpet from the soles of his shoes, even if it is taahir (pure). 

Fataawa al-Lajnah al-Daa’imah, 6/213, 214 

Shaykh Ibn Baaz (may Allaah have mercy on him) was asked: What is the ruling on praying in shoes? 

He replied: 

The ruling is that it is mustahabb after checking to make sure they are clean, because the Prophet (peace and blessings of Allaah be upon him) used to pray in his shoes, and because the Prophet (peace and blessings of Allaah be upon him) said: “The Jews and Christians do not pray in their khufoof (leather socks) or shoes, so be different from them.” But if a person prays barefoot, that does not matter, because it is proven that the Prophet (peace and blessings of Allaah be upon him) also prayed barefoot sometimes. 

If the mosque is furnished with carpets, it is better to take the shoes off, so as to avoid making the carpets dirty or putting other Muslims off the idea of prostrating on it. End quote. 

Majmoo’ Fataawa Ibn Baaz. 

Shaykh al-Albaani (may Allaah have mercy on him) said: I have advised our Salafi brothers not to be so strict concerning this issue – i.e., praying in shoes in the mosques – because there is a difference between the mosques nowadays which are furnished with fine carpets, and the Prophet’s Mosque in the early days of Islam. I gave them the analogy of another example from the Sunnah, where in another story the Prophet (peace and blessings of Allaah be upon him) ordered the one who needed to spit whilst praying to spit to his left or beneath his feet. This was acceptable because the floor in the mosque where the person had to spit was made of sand or pebbles. But nowadays the prayer-hall of the mosque is furnished with carpets, so do they say that it is permissible to spit on the carpets?! Both cases are the same. End quote. 

What Shaykh al-Albaani (may Allaah have mercy on him) had previously been said by Imam Ahmad (may Allaah have mercy on him). 

Ibn Rajab (may Allaah have mercy on him) narrated in Fath al-Baari that Bakr ibn Muhammad said: I said to Abu ‘Abd-Allaah (i.e., Imam Ahmad ibn Hanbal): What do you think about a man spitting in the mosque then rubbing it with his foot? He said: The hadeeth refers to a different situation. He said: The mosques now have mats spread on the ground  and they are not as they used to be. If he wants to spit whilst he is praying, then he may spit to his left, if the spittle will fall outside the mosque. If he is inside the mosque and he cannot make his spittle land outside the mosque, then he should spit into his garment. End quote. 

So he stated that one should only spit in the mosque and rub it with one's foot if the mosque is not carpeted. 

If it is difficult to take off one's shoes, as in the case of boots worn by the military, then they may pray in their shoes, subject to the condition that they ensure that they are clean. 

The scholars of the Standing Committee were asked: 

What is the ruling on entering the mosque with shoes, especially since the military are required by their work to wear their boots all the time, but the mosques are carpeted? 

They replied: 

It is permissible to enter the mosque wearing shoes and to pray wearing them, if they are clean and pure, but they should be checked when entering the mosque to make sure there is no dirt on them. End quote. 

Fataawa al-Lajnah al-Daa’imah, 6/215, 216  may Allah assist us