´It was narrated from Ibn 'Umar that the Prophet said, concerning a man who had a wife and he divorced her, then she married another man who divorced her before consummating the marriage with her, and (it was asked) whether she could go back to her first husband:` "No, not until she tastes his sweetness."
Related hadith on this topic
Explanation & Benefits
Hafiz Muhammad Ameen
From this it is understood that merely contracting a marriage (nikah) with a second husband is not sufficient; rather, consummation (sexual intercourse) is necessary. In addition, it is also necessary that the marriage be contracted with the intention of a regular, settled marital life. Without these two conditions, she does not become lawful (halal) for the first husband.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3443
Hafiz Muhammad Ameen
It is understood from this that in this issue, valid seclusion (khalwah sahihah) does not take the place of intercourse (jima‘), even though in some other matters, valid seclusion is considered equivalent to intercourse. Valid seclusion (khalwah sahihah) is when the husband and wife are alone together in privacy, and there is no legal (shar‘i), medical, or moral impediment to intercourse.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3444
Maulana Ataullah Sajid
Benefit:
By "pleasure" is meant intercourse, that is, the act of conjugal relations, as has been detailed in the previous points.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 1933