Bukhari

Hadith Commentary:
There appears to be an apparent contradiction between the narration from Abdullah ibn Umar (radi Allahu anhu) and this narration regarding the number of degrees (darajat).

The noble hadith scholars (muhaddithin) have reconciled this in several ways:
➊ Imam Tirmidhi (rahimahullah) has given preference to the narration mentioning twenty-five degrees, and has counted the narration with twenty-seven degrees among the unique and rare reports (munfaridat wa ghara'ib) of Ibn Umar (radi Allahu anhu).
➋ The narration with the lesser number should be understood as referring to the initial stage, and the narration with the greater number as the final stage, because it is far from Allah’s mercy that He would give something and then take it back.
➌ In the silent (sirri) prayers, there is the virtue of twenty-five degrees, while in the audible (jahri) prayers, there is superiority of twenty-seven degrees.
➍ This difference in degrees is based on the number of worshippers being few or many. If the worshippers are few, then there is a reward of twenty-five degrees; if they are many, then the reward increases to twenty-seven degrees.
➎ The increase or decrease in reward also depends on the sincerity (ikhlas), piety (taqwa), and humility (khushu‘, khudu‘) of the one praying in congregation, i.e., the difference in degrees is based on differing circumstances.
➏ Since there is an addition in the narration of Ibn Umar (radi Allahu anhu), and the addition of a trustworthy narrator (thiqa) is accepted, therefore the narration of Ibn Umar (radi Allahu anhu) mentioning twenty-seven degrees is to be given preference.
➐ In every prayer there are twenty-five degrees, and in Fajr and Asr there are twenty-seven degrees, because in these two prayers the angels are present.
➑ This difference in degrees is based on the distance of the mosque; the farther the mosque, the greater the reward for going to pray in it.

(Fath al-Bari: 2/173)
And Allah knows best.

560. Commentary:
That is, the virtue of prayer in the wilderness is doubled. It is also understood from this that if a person, while alone in the wilderness, gives the adhan and iqamah and then performs the prayer, it is considered as congregation (jama‘ah).