Is it possible for anyone other than the prophets to reach the degree of khullah (intimate friendship) in the love of Allah Almighty, if he loves no one but Him, or if he achieves what qualifies him for that?

Khullah (intimate friendship) is a more specific form of mahabbah (love), and it does not admit partnership or rivalry. Allah has exclusively bestowed it upon two of His creations: Ibrahim and Muhammad, peace be upon them. It is an active attribute firmly established for Allah through the Qur'an, the Sunnah, and the consensus of the Ahl al-Sunnah, and it must be affirmed for Allah in a manner befitting His majesty. The difference between Allah taking a servant as a khalil and a servant taking Allah or creation as a khalil is as follows: Allah taking a servant as a khalil is exclusive to Ibrahim and Muhammad, whereas a servant taking his Lord as a khalil is possible for whomever Allah grants success. Furthermore, the Companions taking the Prophet as a khalil does not contradict the Prophet's denial of taking anyone other than his Lord as a khalil.