What is the ruling on a man caressing his wife who is making up for missed fasts (qada'), and inserting his fingers into her vagina?

The relationship between a husband and his wife during an obligatory fast, such as Ramadan, is similar to his relationship with food and drink. It is forbidden to approach her for the purpose of fulfilling desire, such as kissing or touching the private parts with lust, as this risks invalidating the fast.

As for a supererogatory fast, it is not forbidden to break it. However, it is not advisable to engage in hugging, kissing, or touching, as it may invalidate the fast or diminish the reward.

If one kisses his wife or engages in foreplay with her and semen is ejaculated, his fast is invalidated by consensus. He must make up for it with repentance if it was an obligatory fast, and it is recommended to make up for it if it was a supererogatory fast. However, if madhy (pre-seminal fluid) is discharged, scholars have differed, and the stronger opinion is that the fast is not invalidated. Nevertheless, it is preferable to make up for that day to avoid the اختلاف (disagreement among scholars). If one kisses and neither semen nor madhy is discharged, then his fast is valid.

Therefore, if nothing was discharged from either of you, your fast is valid. However, do not repeat this during an obligatory fast for fear of ejaculation or intercourse. Whoever engages in intercourse during the daytime in Ramadan must pay a major expiation. Invalidating an obligatory fast is forbidden, and there is no expiation for it except in Ramadan. Invalidating a supererogatory fast carries no sin.