Assalamu alaikum wa rahmatullahi wa barakatuhu.
I have two questions:
1) I had my fardh ghusl just before Asr time whilst fasting. Will my fast be valid?
2) Can I gargle in fardh ghusl whilst fasting?
بسم الله الرحمن الرحيم
In The Name Of Allah, The Most-Gracious, The Most-Merciful
Fasting is to abstain during the day from eating, drinking and sexual intercourse, along with the intention of fasting. Therefore, having ghusl during fasting hours will not affect your fast, so long as you did not swallow water.
Secondly, madmadah (gargling) and istinshaaq (drawing water into the nose), as well as wetting the whole body, is fardh components of ghusl. Gargling with water does not break the fast. However, care should be taken that no water is swallowed. This is done by ensuring that madmadah and istinshaaq is not exaggerated, but only gargled to wet the mouth and drawn in the nose sufficiently to wet the inside of the nose.
Only Allah knows best
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Al-Hidayah, Imran Nyazee Translation, Page 361
 Ibid, Page 366