Is it permissible to perform ‘umrah repeatedly? How long should there be between ‘umrahs?

There is nothing wrong with repeating ‘umrah. The Prophet
(peace and blessings of Allaah be upon him) encouraged us to do ‘umrah
and he did not define the time period that should elapse between two
‘umrahs. 

Ibn Qudaamah said in al-Mughni: 

There is nothing wrong
with doing ‘umrah several times in the year. That was narrated from ‘Ali,
Ibn ‘Umar, Ibn ‘Abbaas, Anas, ‘Aa’ishah, ‘Ata’, Tawoos, ‘Ikrimah and
al-Shaafa’i, because ‘Aa’ishah did ‘umrah twice in one month on the command
of the Prophet (peace and blessings of Allaah be upon him). And the
Prophet (peace and blessings of Allaah be upon him) said: “From one
‘umrah to another is an expiation for whatever (sins) come between them.”
Agreed upon.  

Shaykh Ibn Baaz was asked in Majmoo’ al-Fataawa
(17/432): Is it permissible to perform ‘umrah repeatedly in Ramadaan,
seeking the reward for that?

 He replied: 

There is nothing wrong with that. The Prophet (peace and
blessings of Allaah be upon him) said: “From one ‘umrah to another is an
expiation for whatever (sins) come between them, and an accepted Hajj brings
no less a reward than Paradise.” Narrated by al-Bukhaari, 1773; Muslim,
1349. 

If a person does ‘umrah three or four times, there is nothing
wrong with that. At the time of the Prophet (peace and blessings of
Allaah be upon him), at the Farewell Pilgrimage, ‘Aa’ishah (may Allaah be
pleased with her) did ‘umrah twice within a space of less than twenty days. 

And the Standing Committee was asked (11/337): 

I live in a town 100 kilometers away from Makkah. In Ramadaan
every year I go to Makkah for ‘umrah, and I pray Jumu’ah and ‘Asr there,
then I go back to my town. I discussed that with some of my brothers and
they said that it is not permissible to do ‘umrah every week in Ramadaan. 

They replied: 

If the situation is as you describe, that is permissible,
because there is no text that specifies the length of time that should
elapse between one ‘umrah and the next. 

Some scholars are of the
view that time should be allowed between two ‘umrahs for hair to grow that
the pilgrim can shave in the second ‘umrah. This time period is
approximately one week or ten days. 

Shaykh Ibn ‘Uthaymeen said in al-Sharh al-Mumti’
(7/242): 

Imam Ahmad said: he should not do ‘umrah until his head has
turned black with hair. 

Based on this, what many
people do nowadays of performing ‘umrah repeatedly, especially in the month
of Ramadaan every day, or once each day and once each night, is contrary to
what the salaf used to do. 

Ibn Qudaamah said in al-Mughni: 

‘Ali (may Allaah be pleased with him) said (‘umrah may be
done) once each month. When his hair had grown back, Anas would go out and
do ‘umrah again. Both reports were narrated by al-Shaafa’i in his Musnad.
‘Ikrimah said: He should do ‘umrah when his hair can be shaved by the razor.
‘Ata’ said: If he wishes he can do ‘umrah twice each month. Ahmad said: If
he does ‘umrah, then he has to shave his head or cut his hair. In ten days
he can shave his head.  

Shaykh al-Islam Ibn Taymiyah said in Majmoo’ al-Fataawa,
26/45: 

What Ahmad stated is that it is not recommended to repeat
‘umrah often from Makkah or elsewhere, rather one should allow time in
between for the hair to grow back so that it can be shaved.