It is reported in many hadiths that the Prophet (peace and blessings be upon him) entered the Ka`bah and performed Prayer therein, and so did some of the Prophet’s great Companions (may Allah be pleased with them). So, there is nothing from entering the Ka`bah and performing Prayer therein to trigger pessimism.
Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, states: “It is proven that the Prophet (peace and blessings be upon him) entered the Ka`bah and performed Prayer therein, and so did some of the Prophet’s great Companions (may Allah be pleased with them). There are many hadiths reported in this concern in Al-Bukhari and Muslim. Also, An-Nawawi stated in his book Al-Idah: “It is recommendable for one to enter the Ka`bah bare-footed and offer Prayer therein. It is better to pursue the spot where the Prophet (peace and blessings be upon him) used to perform Prayer. On entering the Ka`bah, the Prophet (peace and blessings be upon him) used to walk from his entrance until there were about three cubits between him and the opposite wall and perform Prayer, as recorded in Al-Bukhari. This can be done on condition that no harm is inflicted on the person or on others. If there is any such harm, one should not enter the Ka`bah.”
As for the reward for entering the Ka`bah, there are many hadiths. Some of them can be traced back to the Prophet (peace and blessings be upon him), while others have their chain of transmission cut before it reaches up to the Prophet (peace and blessings be upon him). Among these hadiths is one that reads: “Whoever enters the Ka`bah and performs Prayer therein acquires a reward and one of his sins is expiated.”
Scholars of the four well known schools of Fiqh have agreed that it is recommendable to enter the Ka`bah, and Imam Malik saw it is, moreover, recommendable to increase the times of entering the Ka`bah. This indicates that there is nothing wrong, nor are there any evil omens, in entering the Ka`bah. Muslims even used to overcrowd on entering the Ka`bah before its door was built higher than the ground of the mosque. After that, such overcrowds decreased and it was then organized so that no harm would come to people and nothing might violate the sacredness of the Ka`bah (Tarikh Al-Ka`bah Al-Mu`azhzhamah, pp. 346-361).
However, those who cannot enter the Ka`bah to perform Prayer therein can pray in Hijr Isma`il, as it is reported by Ahmad with a good chain of transmission that `A’ishah (may Allah be pleased with her) said, “O Messenger of Allah, all your wives have entered the Ka`bah except me.” The Prophet (peace and blessings be upon him) said, “Then summon Shaibah (son of `Uthman ibn Talha; guardian of the Ka`bah who had its key), so that he can open the door for you.” So she sent to Shaibah who said, “We couldn’t ever open the door of the Ka`bah at night, neither before nor after the advent of Islam.” Hence, the Prophet (peace and blessings be upon him) said, “Pray in the Hijr, as your people have left part of the Ka`bah when they built it.” This means that when the people of the Quraish rebuilt the Ka`bah, they did not include the Hijr within the boundaries of the Ka`bah itself, though it was originally part of it. So performing Prayer in Hijr Isma`il is considered as performing prayer inside the Ka`bah.”