Prayer in congregation may be held with two people, an imam and a follower

Yes, two people are enough to pray in congregation, whether
that is in the house or elsewhere. Imam al-Bukhaari (may Allaah have mercy
on him) said: “Chapter: Two or more form a congregation (jamaa’ah).” Then he
narrated the hadeeth of Maalik ibn al-Huwayrith (may Allaah be pleased with
him), that the Prophet (peace and blessings of Allaah be upon him)
said: “When the time for prayer comes, give the adhaan and iqaamah then let
the oldest of you two lead you in prayer.” (al-Bukhaari, 658). 

Al-Haafiz ibn Hajar (may Allaah have mercy on him) said:
“Chapter: Two or more form a congregation”: this heading was narrated in a
hadeeth which was narrated via weak isnaads, which said that the Prophet
(peace and blessings of Allaah be upon him) saw a man praying by
himself and said: “Will not a man perform an act of charity for him and pray
with him?” So a man stood up and prayed with him, and he said: “These two
are a congregation (jamaa’ah).” 

The story mentioned – apart from the words, “These two are a
congregation” – was narrated by Abu Dawood and al-Tirmidhi with a different,
saheeh, isnaad. 

He also said: 

This (the hadeeth of Maalik ibn al-Huwayrith (may Allaah be
pleased with him)) may be understood as meaning that the smallest a
congregation can be is an imam and one follower, which is more general in
meaning than saying that the follower may be a man or a boy or a woman. 

The hadeeth referred to by al-Haafiz is narrated by Abu
Dawood (554) who classed it as saheeh. The report is as follows: It was
narrated from Abu Sa’eed al-Khudri (may Allaah be pleased with him) that the
Messenger of Allaah (peace and blessings of Allaah be upon him) saw a
man praying on his own and said: “Why doesn’t a man perform an act of
charity for him and pray with him?” Classed as saheeh by al-Albaani in
Saheeh al-Jaami’, 2652. 

It says in ‘Awn al-Ma’bood: so that he may attain the
reward of praying in congregation, so it will be as if he gave him charity. 

It was narrated from Ubayy ibn Ka’b (may Allaah be pleased
with him) that the Messenger of Allaah (peace and blessings of Allaah
be upon him) said: “… for a man to pray with another man is better than his
praying alone, and for a man to pray with two other men is better than his
praying with one man. The more there are, the more beloved that is to
Allaah.” Al-Nasaa’i, 843; Abu Dawood, 554; classed as saheeh by al-Albaani
in Saheeh al-Jaami’, 2242. 

But it should be noted
that what is required of men is to offer the prayers in congregation in the
mosque; it is not permissible to offer the obligatory prayers at home,
whether in congregation or alone, unless one has an excuse. 

The Standing Committee was asked: If two people pray together
is that a jamaa’ah (congregation) or not? 

They replied: If two or more people pray together, that is a
congregation, but the more people there are, the better; it should also be
noted that prayers in congregation should be offered in the mosque. 

Fataawa al-Lajnah al-‘Daa’imah,
7/289. 

Shaykh Ibn ‘Uthaymeen
(may Allaah have mercy on him) was asked about some people who prayed in
congregation at home. He said: 

We advise them to fear Allaah and to pray in congregation
with the Muslims in the mosque, because the most correct scholarly view
concerning this matter is that it is obligatory to offer prayers in
congregation in the mosque, unless one has an excuse. The Prophet
(peace and blessings of Allaah be upon him) said: “I thought of ordering
that the iqaamah be given, then I would order a man to lead the people in
prayer, and I would take some men carrying bundles of wood and go to people
who did not attend the prayer, and burn their houses down on them.” See
al-Bukhaari, 644; Muslim, 651. 

Those people may be have been offering the prayers in
congregation in their own places, but the Prophet (peace and blessings
of Allaah be upon him) wanted them to pray with the congregation which was
performing the prayer in the manner prescribed in sharee’ah, and the
congregation which sharee’ah says one should pray with is those who pray in
the mosques, the mosques to which they are called when the time for prayer
comes. Hence ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) said:
“Whoever would like to meet Allaah tomorrow as a Muslim, let him offer these
prayers regularly where the call for them is given.” The word haythu (where)
refers to place, i.e., let him offer them regularly in the place from which
the call to prayer is given. 

Fataawa al-Shaykh Ibn ‘Uthaymeen,
15/19 

For more information and evidence on this matter, please see
question no. 8918
and 40113.