The Messenger of Allah (May peace be upon him) made a concession in the early days of Islam on account of the paucity of clothes that one should not take a bath if one has sexual intercourse (and has no seminal emission). But later on her commanded to take a bath in such a case and prohibited its omission.  

أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ ﷺ إِنَّمَا جَعَلَ ذَلِكَ رُخْصَةً لِلنَّاسِ فِي أَوَّلِ الإِسْلاَمِ لِقِلَّةِ الثِّيَابِ ثُمَّ أَمَرَ بِالْغُسْلِ وَنَهَى عَنْ ذَلِكَ  

The verdict that water (bath) is necessary when there is emission given by the people (in the early days of Islam) was due to the concession granted by the Messenger of Allah in the beginning of Islam. He then commanded to take a bath (in such a case). Abu Dawud said : By Abu Ghassan is meant Muhammad b. mutarrif.  

أَنَّ الْمَاءَ مِنَ الْمَاءِ كَانَتْ رُخْصَةً رَخَّصَهَا رَسُولُ اللَّهِ ﷺ فِي بَدْءِ الإِسْلاَمِ ثُمَّ أَمَرَ بِالاِغْتِسَالِ بَعْدُ  

when anyone sits between the four parts of a woman and the parts (of the male and female) which are circumscised join together, then bath becomes obligatory.  

أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا قَعَدَ بَيْنَ شُعَبِهَا الأَرْبَعِ وَأَلْزَقَ الْخِتَانَ بِالْخِتَانِ فَقَدْ وَجَبَ الْغُسْلُ  

The Messenger of Allah (May peace be upon him) said : water (bath) is necessary only when there is seminal emission. And Abu Salamah followed it.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ الْمَاءُ مِنَ الْمَاءِ وَكَانَ أَبُو سَلَمَةَ يَفْعَلُ ذَلِكَ