We praise Allah, may He be glorified and exalted, for having blessed you with the ability to do Hajj and we ask Him to accept it from you and that you have returned home as on the day your mother bore you, free of sin for He is Most Generous, Most Kind.
As for what you have done of giving up music and teaching dance, this is one of the blessings of obedience and gratitude for blessings. The Muslim should start a new leaf every day and turn his back on his past bad deeds, so that he will be a repentant slave, purifying his heart of sin and doubt.
We advise you to carry on with what you are doing, for it is good and righteous. You should repent from what you have done in the past and turn to Him, for repentance erases what came before it and washes away sins from one’s record. This is by the help and guidance of Allah to you, so give thanks abundantly to Him.
With regard to the answer to your first question:
If aerobic exercise and swimming are done with the accompaniment of music, and the music is part of the programme, then doing this kind of exercise in this way is haram. The prohibition is further emphasised for the one who teaches that to people and promotes it among them, thus becoming a promoter of sin and misguidance. May Allah keep us and you safe and sound.
But if the exercise is free of music – which is not too difficult – and people’s ‘awrahs are covered and there is no free mixing, then it is like any other kind of exercise or sport and there is no blame on the one who does it, especially if there is a direct physical benefit.
But it is haram to teach it to anyone who it is thought will misuse it and change it from being free of reprehensible matters, and do it in the original prohibited form.
Based on that, there is nothing wrong with you doing this exercise so long as you are confident that you will not go back or long for what was done in the past. We recommend you to do it without music in your head, and to get yourself used to doing that regularly, until the effect is gone altogether. This is what is meant by proper avoidance mentioned in the hadeeth of Abu Hurayrah (may Allah be pleased with him), who said that he heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Whatever I forbid you to do, avoid it.” Narrated by al-Bukhaari (6858) and Muslim (1337).
It is essential to give up sin and to give up that which will remind one of it or cause one to go back to it.
We also advise you to have high aspirations and aim for the top, for the ummah is in need of people who will lead it in the way of revival and rid it of obstacles that hinder its progress, seeking thereby the reward of Allah, based on sound intention (i.e., pleasing Allah). You should persist in that and seek the help of Allah and put your trust in Him. The one who strives hard and does his utmost will not be disappointed. Allah, may He be exalted, says (interpretation of the meaning): “As for those who strive hard in Us (Our Cause), We will surely guide them to Our Paths (i.e. Allah’s Religion - Islamic Monotheism). And verily, Allah is with the Muhsinoon (good doers)” [al-‘Ankaboot 29:69].
With regard to the answer to your second question:
The evidence for the prohibition on singing is plentiful and we have discussed this issue a great deal on this website. Please see the answers to questions no. 5000 and 122790 for some responses to those who raise objections.
With regard to the words of Ibn Mas‘ood, they are among the greatest evidence quoted by those who regard it as prohibited. The same commentary was narrated from Ibn ‘Abbaas and Ibn ‘Umar, so we do not know how come he is regarded as being one of those who say that it is permissible.
The basic principle is that the seeker of knowledge should adhere to the views of the earlier generations as much as he can, so how about if these earlier generations are from among the first generation of whose virtue and goodness the Prophet (blessings and peace of Allah be upon him) spoke?
How about if their evidence is stronger, more plentiful, and clearer?
The prohibition on singing has been narrated from the Sahaabah and the four imams; some of the scholars narrated that there was consensus on this matter, and those who differ concerning it are few, such as Ibn Hazm az-Zaahiri, al-Ghazaali, ash-Shawkaani and others. We do not doubt that their intention was to seek the correct view, but we think that they went against the correct view and they took the weaker view as being more correct.
It should be noted that those who say that singing is permissible are unanimously agreed that it is prohibited if it involves free mixing, promiscuity or indecent speech as is the case with singing and music nowadays.
In the case of al-Ghazaali (may Allah have mercy on him), he did not regard it as permissible to listen to singing in general terms, as he said in his book Ihya’ ‘Uloom ad-Deen (3/272), after saying that unaccompanied singing or singing that is accompanied by the hand-drum or pipes is permissible:
“But from this (permissibility) is excepted those idle instruments of music, both stringed instruments and pipes, which the text indicates are forbidden; not because of their giving pleasure, since if it were on that account all the things by which man receives pleasure would be judged like these. But wine was forbidden, and man’s excessive addiction to it required, to wean him from it, that the command should extend at first so far as to involve the breaking of wine jars. And, along with wine, was forbidden all that was a badge of people who drank it, in this case stringed instruments and pipes only. So these being forbidden was a consequence, just as being alone with a woman not a relative is forbidden, for being so alone may lead to (haraam) sexual intercourse; and seeing the thigh is forbidden, for the thigh is near to the pudenda [‘awrah]; and a little wine is forbidden, even though it does not intoxicate, because it invites to intoxication. There is no forbidden place [haram, a sanctuary to which access is restricted] but it has a sacred precinct [hima] which surrounds it, and the decree of prohibition extends to the sacred precinct in order that it may be a protection for the forbidden place [or sanctuary] and a defence to it and a private enclosure [or “buffer zone”], as [the Prophet] (blessings and peace of Allah be upon him) said: “Verily every king has a private enclosure, and the private enclosure of Allah is the things which He has forbidden.”
It says in al-Waseet (7/350):
Musical instruments and stringed instruments are prohibited, because they make one long for drink, and they are the symbol of drink [i.e., the people who drink wine]. So it is prohibited to resemble them. As for the daff (hand-drum), if it does not have any jingles, it is permissible; hand-drums were beaten in the house of the Messenger of Allah (blessings and peace of Allah be upon him). End quote.
The evidence quoted by those who regard it as permissible was critiqued by a number of scholars, researchers and seekers of knowledge; we refer you to the following article, which discusses in detail the evidence they rely on, and highlights its shortcomings:
And Allah knows best.