When entering Masjidil Haram, step with the right foot and say: 'Bismillah, wassalatu wassalamu 'ala Rasulillah. Allahumma iftah li abwaba rahmatik. Allahumma zid hadhal-bayta tashrifan wa ta'ziman wa takriman wa mahabah.' This combines the general masjid doa with honor for the Sacred House.
بِسْمِ اللَّهِ، وَالصَّلَاةُ وَالسَّلَامُ عَلَى رَسُولِ اللَّهِ. اللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ. اللَّهُمَّ زِدْ هَذَا الْبَيْتَ تَشْرِيفًا وَتَعْظِيمًا وَتَكْرِيمًا وَمَهَابَةً
Bismillah, wassalatu wassalamu 'ala Rasulillah. Allahumma iftah li abwaba rahmatik. Allahumma zid hadhal-bayta tashrifan wa ta'ziman wa takriman wa mahabah.
Meaning: In the name of Allah, and blessings and peace be upon the Messenger of Allah. O Allah, open for me the doors of Your mercy. O Allah, increase this House in honor, reverence, dignity, and awe.
Source: Sahih Muslim #713Masjidil Haram is the most sacred masjid in Islam. Nabi (shallallahu alaihi wa sallam) said: 'One shalat in this masjid of mine (Madinah) is better than a thousand shalat elsewhere, except al-Masjidil Haram. And one shalat in al-Masjidil Haram is better than one hundred thousand shalat elsewhere' (Musnad Ahmad 14694). Entering it is a moment of profound spiritual significance.
بِسْمِ اللَّهِ، وَالصَّلَاةُ وَالسَّلَامُ عَلَى رَسُولِ اللَّهِ. اللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ. اللَّهُمَّ زِدْ هَذَا الْبَيْتَ تَشْرِيفًا وَتَعْظِيمًا وَتَكْرِيمًا وَمَهَابَةً
The Prophet (peace be upon him) said: 'When one of you enters the mosque, let him send salah upon the Prophet (peace be upon him) and say: Allahumma iftah li abwaba rahmatik. And when he leaves, let him say: Allahumma inni as'aluka min fadlik.'