If the pilgrim who is doing tamattu‘ does not fast the three days until he leaves Makkah

Firstly:

The fuqaha’ are
agreed that if the pilgrim who is doing tamattu‘ cannot afford a hadiy, he
must fast three days during Hajj and seven days after he returns home,
because Allah, may He be exalted, says (interpretation of the meaning):

“but
if he cannot afford it, he should observe Saum (fasts) three days during the
Hajj and seven days after his return (to his home), making ten days in all”

[al-Baqarah
2:196].

End quote from
al-Mawsoo‘ah al-Fiqhiyyah (14/12-13)

Secondly:

What should be
done is not to delay fasting the three days beyond the days of at-Tashreeq.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:

It is
permissible to fast the three days during the days of at-tashreeq, which are
the eleventh, twelfth and thirteenth of Dhu’l-Hijjah, and it is permissible
to fast them before that, after entering ihram for ‘umrah. It is permissible
to fast these three days consecutively or separately, but they should not be
delayed beyond the days of at-tashreeq. As for the remaining seven days, he
should fast them when he returns to his family; if he wishes he may fast
them consecutively, and if he wishes he may fast them separately.

End quote from
Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen (24/376)

If he did not
fast the three days during Hajj, then he must make them up, whether he
omitted to fast them because of an excuse or otherwise. But if he did not
have an excuse, then he has done something wrong and must repent to Allah,
by regretting what he did and resolving not to do it again.

The scholars of
the Standing Committee for Issuing Fatwas said:

If the pilgrim
who is doing tamattu‘ is not able to offer the sacrifice and is not able to
fast during the days prescribed, then he must fast when he is able to, even
if that is after he returns to his country.

End quote from
Fataawa al-Lajnah ad-Daa’imah (10/410)

Shaykh Ibn
‘Uthaymeen said:

If a person
delays fasting the three days that should be fasted during Hajj, until he
has finished his Hajj, with no excuse, does he have to offer a fidyah? The
correct view is that he does not have to, and it is strange that the fuqaha’
(may Allah have mercy on them) said that he does have to offer a fidyah,
when he could not afford it in the first place. Moreover, because he could
not afford a hadiy, fasting became obligatory in his case, therefore we say
that the fasting must be done during Hajj, but if he delays it – especially
if he had an excuse – then it must be made up, like Ramadan.

End quote from
ash-Sharh al-Mumti‘ (7/180)

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) was also asked about a man who did
Hajj tamattu‘ and there was a fire in which his things and his money were
burned in the tent, so he did not offer a fidyah; does he have to do
anything?

He replied:

We do not know
what the brother did: did he fast? Because the fire happened on the eighth
day, so if the Day of Sacrifice came, and he did not have anything, then let
him fast the eleventh, twelfth and thirteenth, then when he goes back to his
family, he may fast the remaining seven days, because Allah, may He be
Blessed and exalted, says (interpretation of the meaning):

“and
whosoever performs the Umrah in the months of Hajj, before (performing) the
Hajj, (i.e. Hajj-at-Tamattu and Al-Qiran), he must slaughter a Hady such as
he can afford, but if he cannot afford it, he should observe Saum (fasts)
three days during the Hajj and seven days after his return (to his home)”

[al-Baqarah
2:196].

If he did not do
that, then now he must repent to Allah and fast ten days, three to make up
(what he should have done during Hajj) and seven other days as prescribed.

End quote from
Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen (22/208)

The scholars of
the Standing Committee for Issuing Fatwas were asked:

I did the
obligatory pilgrimage several years ago, but I did not offer a sacrifice on
the Day of Eid, because of lack of means. I was told that I could fast three
days during Hajj and seven days when I went back to my country, but then I
forgot, so I did not make up the three days during Hajj, or the seven days
after I returned home. What should I do? May Allah reward you with good.

They replied:

You have to fast
the ten days in your country, if you were doing qiraan (‘umrah and Hajj
together, entering ihram once and remaining in ihram until the end of Hajj)
or tamattu‘ (entering ihram for ‘umrah, exiting ihram, then entering ‘ihram
again for Hajj).

End quote from
Fataawa al-Lajnah ad-Daa’imah (11/388)

As you have
fasted the ten days, you have done what was required of you, and we ask
Allah, may He be exalted, to accept it from you.

And Allah knows
best.