Is the intention for major ablution (ghusl), meaning the washing away of ritual impurity (janabah), valid and sufficient when performing ghusl from janabah if it is made in the heart?

The reality of intention (niyyah) is purpose, and its place is the heart. Therefore, whoever wishes to perform an act for which intention is a prerequisite must intend with their heart what they wish to do. The description of the intention is to intend to remove the ritual impurity (hadath) or to purify from the hadath, and whichever one is intended suffices. So, if you intend to perform ghusl (ritual bath) from major ritual impurity (janabah) when you begin it, this is sufficient. And it does not harm you to recall the intention of the greater ablution (wudu' al-akbar) if you believe that it is the removal of ritual impurity or purification from it.