Shaykh Rabee ibn Haadi Al-Madkhalee (hafidahullah) was asked:

What is your advice – Allah preserve you – to the one who has fell into the sea of desires and doubts?

My advice to him is that he repents to Allah and that he brings to mind the statement of Allah:

قُلْ يَا عِبَادِيَ الَّذِينَ أَسْرَفُوا عَلَىٰ أَنفُسِهِمْ لَا تَقْنَطُوا مِن رَّحْمَةِ اللَّهِ إِنَّ اللَّهَ يَغْفِرُ الذُّنُوبَ جَمِيعًا إِنَّهُ هُوَ الْغَفُورُ الرَّحِيمُ

Say: “O ‘Ibadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful. [Az-Zumar: 53]

So if you swam in the sea of disbelief for you is to exit with repentance to Allah (tabaaraka wa ta’aala), therefore upon him is to repent to Allah and return to Allah, the door of repentance is open for all of the servants (of Allah).

Question 7 from Asbaab al-Inhiraaf wa Tawjeehaat Manhajiyyah.